Poor Hot Water Flow - Buy a 40psi Jabsco Par Max 4??

[Richard10002]

I have 2 ways of heating hot water…

1)      a Truma gas air an water heater, which stores about 12 litres of hot water, so not enough for more than one wash in the handbasin, or one lot of washing up – definitely not enough for a shower. This has fed the kitchen basin and shower basin for years, but can be frustrating if there are more than a couple of people wanting a quick wash in the morning, or more than a small amount of washing up.

2)      A Rinnai instant gas water heater which has been connected to the shower only, and worked well.

For ages I have wanted to re jig things so that everything worked off the Rinnai, such that we could have instantaneous and continuous hot water for everything – perhaps with the Truma as a back up.

A couple of weeks ago I added a couple of Speedfit valves and a bit of new pipework such that the Truma is now isolated from the hot water pipework, and the Rinnai feeds the lot. Switching both the valves reverts the system to the Rinnai feeding the shower only and the Truma feeding the basins.

All good, (almost). The Rinnai now provides hot water everywhere. However, the hot water flow is very poor, to the point where it can be so poor that the pump cycles on and off and, as the pressure drops, the Gas to the Rinnai cycles on and off as well. The cold flow is fine.

Given that the flow was fine when the Rinnai was feeding the shower only, and the gas didn't cycle, I'm assuming that the Rinnai is working fine, and can heat enough water to the right temperature if it gets the right flow.

The pump is a Jabsco Par Max 2.9, (cut in at 15psi, cut off at 25psi). I adjusted the accumulator last week such that the cold flow is much better than it used to be, so I think it is pressurised correctly.

During my alterations I must have done something that restricts the flow along the hot water route, (perhaps the valves, which, when open, the hole is much smaller than the 15mm Speedfit pipe), such that increased pressure from the pump might sort things out.

The question is as simple as:

if I got a Jabsco Par Max 4, (cut in at 20psi, cut out at 40psi), would that be likely to improve the hot water pressure enough, without increasing the cold water pressure too much?

[MtB]

The obvious question is you say the Rinnai flames didn't cycle on and off when running the shower before you fiddled with the pump settings, but did you test the shower afterwards too?  Does it still run without the flames cycling on/off?

[Richard10002]

4 minutes ago, Mike the Boilerman said:

The obvious question is you say the Rinnai flames didn't cycle on and off when running the shower before you fiddled with the pump settings, but did you test the shower afterwards too?  Does it still run without the flames cycling on/off?

I knew there would be more information required

Shower works fine - it's a thermostatic control, if that matters. Flames dont cycle, flow remains constant and as good as ever, even when turned up to it's hottest temp, (which is way too hot for a shower).

If it helps, the new valve, that allows hot water to continue beyond the shower to the shower hand basin and the kitchen basin, is after the shower. So I am wondering if the narrowness of the SpeedFit valve is affecting the flow.

[MtB]

1 minute ago, Richard10002 said:

I knew there would be more information required

Shower works fine - it's a thermostatic control, if that matters. Flames dont cycle, flow remains constant and as good as ever, even when turned up to it's hottest temp, (which is way too hot for a shower).

 

I'd be more concerned about the flames cycling on/off with the shower running at lower, normal showering temperature. As you lower the shower temperature ever more, I would expect you to eventually reach a point when the flame cycling begins. 

 

3 minutes ago, Richard10002 said:

If it helps, the new valve, that allows hot water to continue beyond the shower to the shower hand basin and the kitchen basin, is after the shower. So I am wondering if the narrowness of the SpeedFit valve is affecting the flow.

 

Sounds to me as though there is a restriction in the hot pipe somewhere, but it is unlikely to be the speedfit valve. To rule it out, close the valve, disconnect the outlet pipe from the valve, insert a short bit of pipe, open the valve discharging into a bucket and see if the flame cycling remains or vanishes. 

If it vanishes this suggests a restriction further along the plumbing system. See if you can find other places to break the pipe and do the same experiment into a bucket.

[matty40s]

You will probably find that you need a higher bore pipe....22mm or larger feeding the Rinnai. It'd ok to have 15mm from it though.

[Richard10002]

1 hour ago, Mike the Boilerman said:

 

I'd be more concerned about the flames cycling on/off with the shower running at lower, normal showering temperature. As you lower the shower temperature ever more, I would expect you to eventually reach a point when the flame cycling begins. 

As I lower the shower temperature the water temperature remains warm, but becomes too cold for a shower, and the flames continue. Then there comes a point where the flames go out, and the water runs cold. I cant make such a minute adjustment such that the flames cycle.

I cant do your flow test today, but maybe tomorrow, or late next week. I think I'm reassured that the issue could be caused by a restriction of flow, rather than the pump pressure. Just hope I can find it.

[MtB]

8 minutes ago, Richard10002 said:

I think I'm reassured that the issue could be caused by a restriction of flow, rather than the pump pressure. Just hope I can find it.

 

I agree. If the pump works the shower without cycling on and off, we know the pump/Rinnai combination works correctly. Therefore the fault must lie elsewhere. 

[Neil2]

I too doubt the pump will make any difference, I also have a Rinnai and fitted a more powerful pump earlier this year, it made no difference to the hot water flow.

From my experience with the Rinnai I think you may be asking too much of it.  You don't say how far from the water heater the furthest outlet is.  On our boat the pipe to the whb is about 20 feet long and the flow is just about acceptable, but if it was much further away I think it might struggle. 

[Arthur Marshall]

My Rinnai feeds the shower OK as long as I set the temp on the heater and don't try to mix it with cold water.  As soon as I do that the pressure drops and the flame dies. Can be difficult getting the temp right for a shower in the summer when the water in the tank is quite warm as you can't run it down low enough, and in winter it doesn't heat near freezing water enough - my water tank is the front bit of hull so is at the same temperature as the canal.

[smileypete]

As MTB said, full bore valve may well help instead of the speedfit ones, maybe try swapping the latter with an offcut of pipe to see what happens?

Failing that don't overlook that the kitchen and basin taps may be ones designed for a high pressure mains supply and not low pressure/gravity, the cheaper ones tend to be the former. You're pretty lucky that the Rinnai plays OK with the thermostatic mixer as it is.

Edited October 21, 2017 by smileypete

[Richard10002]

On 21/10/2017 at 13:30, Mike the Boilerman said:

Sounds to me as though there is a restriction in the hot pipe somewhere, but it is unlikely to be the speedfit valve. To rule it out, close the valve, disconnect the outlet pipe from the valve, insert a short bit of pipe, open the valve discharging into a bucket and see if the flame cycling remains or vanishes. 

If it vanishes this suggests a restriction further along the plumbing system. See if you can find other places to break the pipe and do the same experiment into a bucket.

Hi Mike,

Did your test - as it happens, the drain for the system is just after the valve which follows the shower connection, so I opened this into a "bucket", and the flow was weak, and the flame cycled.

Pretty sure it's the Speedfit valve.... the internal diameter when opened is tiny compared to the full 15mm bore of the pipe it's connected to:

 

Sorry about the picture size. Could this be the cause? 

I'm wondering if there is a Speedfit valve, or a Hep2o valve, or some other quickfit type valve that has the full 15mm bore, rather than restricting it like the one fitted.

[Tony Brooks]

Warning - if you are forced to go to compression full bore valves please make sure you get a METAL insert for the ends of the plastic pipe. The plastic inserts allow the pipe to shrink from under the olive.

[alan_fincher]

As you have discovered, these only have a very small hole when open.

I returned a number as unsuitable, and bought these instead.

Admittedly moe expensive, but from memory they are either "full bore" or very close to it.

[MtB]

On 28/10/2017 at 14:04, Richard10002 said:

Hi Mike,

Did your test - as it happens, the drain for the system is just after the valve which follows the shower connection, so I opened this into a "bucket", and the flow was weak, and the flame cycled.

Pretty sure it's the Speedfit valve.... the internal diameter when opened is tiny compared to the full 15mm bore of the pipe it's connected to :

Sorry about the picture size. Could this be the cause? 

I'm wondering if there is a Speedfit valve, or a Hep2o valve, or some other quickfit type valve that has the full 15mm bore, rather than restricting it like the one fitted.

 

I'd be surprised, but it is possible. 

The hydraulic resistance of a pipe is inversely proportional to its cross-sectional area, but is also proportional to it's length. Introducing a very short restriction such as your valve is NOT the same as having the whole length of pipe the same small cross section, a concept many people struggle to grasp. It means very short sections of pipe smaller in diameter only have a minimal overall effect on flow. Adding a metre or two of full bore 15mm pipe to the length would probably add much the same hydraulic resistance as adding the valve in your photo. 

To prove or disprove the valve is the problem, turn the pump off, open the valve to drain off the pressure into a bucket, remove the valve then turn the pump ON again. See if the cycling vanishes or persists...

Edited October 28, 2017 by Mike the Boilerman

[Richard10002]

44 minutes ago, alan_fincher said:

As you have discovered, these only have a very small hole when open.

I returned a number as unsuitable, and bought these instead.

Admittedly moe expensive, but from memory they are either "full bore" or very close to it.

One of the reviews from a plumber states:

"" This does what is says on the tin. It is a 15mm ball valve. ie 15mm dia. hole right through! NO REDUCTION IN THE BORE!!!!!!!!!!
Therefore full flow and full pressure. 
BRILLIANT!! ""

I like the sound of that, and for nine quid, it's got to be worth a go!

29 minutes ago, Mike the Boilerman said:

 

I'd be surprised, but it is possible. 

snip

To prove or disprove the valve is the problem, turn the pump off, open the valve to drain off the pressure into a bucket, remove the valve then turn the pump ON again. See if the cycling vanishes or persists...

I'll give this a go before spending the money

[Richard10002]

20 hours ago, Mike the Boilerman said:

 

I'd be surprised, but it is possible. 

The hydraulic resistance of a pipe is inversely proportional to its cross-sectional area, but is also proportional to it's length. Introducing a very short restriction such as your valve is NOT the same as having the whole length of pipe the same small cross section, a concept many people struggle to grasp. It means very short sections of pipe smaller in diameter only have a minimal overall effect on flow. Adding a metre or two of full bore 15mm pipe to the length would probably add much the same hydraulic resistance as adding the valve in your photo. 

To prove or disprove the valve is the problem, turn the pump off, open the valve to drain off the pressure into a bucket, remove the valve then turn the pump ON again. See if the cycling vanishes or persists...

Removed the valve and replaced it with a full bore straight through connector, ran the system. Cold water - good pressure as ever. Hot water - low flow and cycling flames at the Rinnai. So removing the valve has had no effect.

Remembering that the hot flow was fine when fed from the Truma 12l tank, I can't see that the distance of the basins could be an issue. The kitchen basin is probably about a 50/60ft run from front of accommodation and halfway back again, and the bathroom about a 35ft run.

In order to introduce the Rinnai into the system, I've fitted a valve on the hot output of the Truma to isolate it from the hot part of the system, (the cold is still connected to the input side, but I guess/hope that the tank just pressurise an water carries on as ever, evidenced by the fact that the cold flow and pressure is fine). One thought that crosses my mind is that my revised pipework could be causing the hot water to be flowing against itself somewhere, (this definitely happened before I fitted the valve to the hot output from the Truma). I drew a very rough diagram of the pipework as I can see it, thought about it long and hard, and I'm sure that the hot water route from Rinnai via the shower, past the Truma, where it splits to go off to bathroom and kitchen, is a one way trip, if that makes sense. I'll take another look at this and make sure i'm right.

Alternatively, I wonder if the Rinnai causes a restriction, and the fact that is is only about 6 feet to the shower means the flow is fine to the shower, but struggles with the distances to bathroom and kitchen.

Assuming my pipework is correct, I'm finding it hard to see why a pump with higher pressure wont improve things, (not saying anybody is wrong, just struggling to understand - the existing pump pumps between 15psi and 25psi, and flow was fine before my changes. If it pumped at much lower pressures, say between 3psi and 7psi, surely something would be worse and, at some lower pressure, flow would stop?)

 

[Richard10002]

Had a closer look at the Rinnai and it has two controls, 

1) High or Low flame - which does what it suggests. I have it on High flame.

2) Temperature 1-5 - This dial appears to reduce the flow of water, (thus allowing it to heat up more)

I have had the temp dial on 5 to get the hottest water, to then be controlled at the tap. Reducing it to say, 3, increases the throughput, with better flow at the taps, the pump keeps running, but it doesn't get as hot, and probably not hot enough. 4 seems to be a fair compromise of temperature, but the flow is still such that it drops to almost nothing before the pump kicks in and runs for a while before stopping again for a while.

That read a bit confusing, but my sense is that if the pump started at a higher pressure, it would run permanently, thus both the flow and temp would be fine when set on 4.

The Jabsco pump cuts in at 15psi, and out at 25psi, (IIRC). Perhaps if I could find a pump that cuts in at 20psi, things would be improved??

Any thoughts?

 

[Tony Brooks]

Yes. do away with the pump's inbuilt pressure switch and fit one on the pipe like a Square D that allows you to adjust cut out and cut in pressure.  It sounds as if the pressure difference is rather large to me at present.

[Arthur Marshall]

If you're controlling the water temp at the taps, as soon as you turn on the cold you will reduce the water pressure to the Rinnai, and if it's on 5 there probably won't be enough to keep it alight. I find mine gives me a decent shower temp at 3 in summer and 4 in winter, depending on the temp of the water in the tank. My  Rinnai won't run hot and cold taps at the same time on my Jabsco pump, and nor did the one I had before. 

[Richard10002]

1 hour ago, Arthur Marshall said:

If you're controlling the water temp at the taps, as soon as you turn on the cold you will reduce the water pressure to the Rinnai, and if it's on 5 there probably won't be enough to keep it alight. I find mine gives me a decent shower temp at 3 in summer and 4 in winter, depending on the temp of the water in the tank. My  Rinnai won't run hot and cold taps at the same time on my Jabsco pump, and nor did the one I had before. 

My Kitchen and bathroom handbasin taps are both mixers, rather than separate hot and cold taps. I would have thought that moving them towards hot would close off the cold pipe, and open up the hot pipe, (I could be wrong), and vice versa. The flow decreases significantly when they are moved to hot, and becomes "normal" if moved towards cold - so it seems to be all to do with flow/pressure in the hot pipes.

The thermostatic mixer shower works fine with good flow and temp when the Rinnai is set on 5. I can currently "make do" with the temp set at 3 or 4 for the basins but, if playing around with pressure from the pump end of things can improve things, I'll have a go.

[Richard10002]

2 hours ago, Tony Brooks said:

Yes. do away with the pump's inbuilt pressure switch and fit one on the pipe like a Square D that allows you to adjust cut out and cut in pressure.  It sounds as if the pressure difference is rather large to me at present.

Sounds good, except that it's easy for you to say, and gobbledegook to me

1) Jabsco Par Max 2.9 - how do I "do away with the pumps inbuilt pressure switch"?

2) What kind of Square D switch? Can you suggest a specific one that would do the job, (and provide a link  )

3) Are these pressure switches push fit, or would I need to sort out some joints/couplings?

4) There is a Shureflo accumulator Model 181-201 which I mentioned in the OP. Could this be causing an issue? Remove it? etc....

I'm sure fitting a pressure switch is fairly straightforward when it comes to it... 

[smileypete]

On 10/29/2017 at 10:46, Richard10002 said:

Assuming my pipework is correct, I'm finding it hard to see why a pump with higher pressure wont improve things, (not saying anybody is wrong, just struggling to understand - the existing pump pumps between 15psi and 25psi, and flow was fine before my changes. If it pumped at much lower pressures, say between 3psi and 7psi, surely something would be worse and, at some lower pressure, flow would stop?)

All these heaters have a 'water governer' built in, they're effectively a pressure reducing valve set to 1 bar say, and are separate from the temperature/flow control.

So I doubt a higher pressure pump will do it, see post 10. If you're set on another pump you could always try hooking the heater up to a mains standpipe, say 7 bar or less.

Attached is the service manual, see page 10 (actual page 10):

Rinnai58eServiceManual.pdf

Edited November 4, 2017 by smileypete

[MtB]

This is all rather perplexing, but I think you are unclear on just how an instantaneous water heater works (as am I still, but to a lesser degree than you, probably!)

When you turn ON a hot tap, water flows through the heat exchanger where it picks up heat from the gas flames. As you can perhaps imagine, the slower the water flows through the heat exchanger, the more it will be heated. The inverse of this means that if the water flows through the heat exchanger (and therefore from the hot tap too) too quickly, it will be too cool.

So one way for the water heater to regulate the temperature of the hot water is for it to adjust the flow rate through the heat exchanger. Given the size of the gas flame is fixed (ok well there are two fixed sizes usually, low and high, user selectable), the water flow from the hot tap is bound to be slower than the unregulated, unrestricted flow from the cold tap. So the difference in flow you note and seem worried about is correct and normal.

Another way instantaneous water heaters regulate water temperature is to fix the speed of the water through the heat exchanger at a slow rate which produces extremely hot water, and have a user control which bleeds a varying amount of cold water into the output to adjust the temp. Your Rinnai, I think, does this. 

The gas flames turning on and off as you experience is rather perplexing. The gas flame is turned ON by a mechanical device (a diaphragm) that relies on the restriction is water flow through the heat exchanger. When the water flows, the (designed in) restriction in water flow causes a lower water pressure to occur at the outlet of the heat exchanger compared to the inlet pressure. This pressure difference moves the diaphragm to one side which in turn, mechanically opens the valve supplying gas to the burner. So the burner lights. And conversely, when the water flow stops, the pressure difference vanishes, the diaphragm returns to its resting position and the gas flames go out.

So... the perplexing thing is why your pressure difference becomes intermittently too small to keep the diaphragm moved and the gas flame alight, as the pump cycles on and off. My best guess would be a perished diaphragm with a pinhole through it. Now sadly I suspect this is a terminal problem with the Rinnai as I believe they no longer make spares for it. Hopefully I'm wrong here though.

There is a complication here though, and that is overheat protection. I dunno about your Rinnai but my Morcos will all shut the gas flames off if the flow temperature gets too high. I don't yet understand how this mechanism works, and I wonder if this your Rinnai has a similar mechanism designed in, and is coming into operation.

[Tony Brooks]

1 hour ago, Richard10002 said:

Sounds good, except that it's easy for you to say, and gobbledegook to me

1) Jabsco Par Max 2.9 - how do I "do away with the pumps inbuilt pressure switch"?

2) What kind of Square D switch? Can you suggest a specific one that would do the job, (and provide a link  )

3) Are these pressure switches push fit, or would I need to sort out some joints/couplings?

4) There is a Shureflo accumulator Model 181-201 which I mentioned in the OP. Could this be causing an issue? Remove it? etc....

I'm sure fitting a pressure switch is fairly straightforward when it comes to it... 

1 - disconnect the usually red wires and then connect the new switch to the red wire that runs into the motor - the "red wire" may be black or black with a  white trace.

2 - I think its an Ebay job, you need one with both the cut in and cut out pressures adjustable,

3 - Those I have used have a female thread for connecting to suitable adaptors and then a T fitting. I would use a tap wall plate to  support the switch and then whatever you want to connect the the T that you fit in the pipework be it compression or push fit.

4 - I can't see it being a problem.

What I find strange is that you say the outlet volume drops to very little before the pump comes back on on each pump cycle. That sounds more like a pressure switch problem than a straight forward lack of presser.

If the flow from any outlets is the same or greater than the pump's displacement then there will be no cycling because the pressure can not build up to the cut out pressure. If the outlet flow is less then the pressure will build up so the pump cycles on and off although the accumulator should lengthen the cycling periods. (That's if it is an accumulator and not the identical thing pressurised as an expansion vessel). You seem to be saying that while the pump runs the heater works as it should but when the pump stops the outflow diminishes to a trickle before the pump cuts back in so the heater shuts down. That makes little sense to me apart from having stick pressure switch that is reluctant to turn back on or a huge  restriction to flow so once the pump turns off the pressure before the heater takes a long time to drop to teh cut in pressure. I find this hard to understand.

I think the pressure of the various pumps is a function of the pressure switch, have you tried adjusting it to increase the cut out and probably the cut in pressures?

 

[smileypete]

One more thing, check any filter washers on the inlet to the heater or taps downstream, any blockage won't help.

While at it you could also do an 'open flow' check at the tap connection, this should confirm the taps are the problem.

Edited November 4, 2017 by smileypete