Cold then Hot then cold then hot ????? (1 Viewer)

[chippy63]

So one for all the technically minded out there.

Have a rapido with a shurflo pump pressurised system.

Assuming there is hot water in the boiler & system is pressurised the scenario is turn mixer tap to cold cold water flows cold then pump kicks in water flows hot, pump goes off water flows cold, this constantly cycles.this is both bathroom tap & shower any ideas why & how to stop it ???.

TIA

Karl

 

[pappajohn]

Restriction in the system causing the pump to cycle, but if the tap is set to cold you shouldn't get any hot regardless of what the pump is doing.

 

[funflair]

What about the kitchen tap and is the shower a stand alone tap or is it just off the bathroom mixer tap. Has it just started doing this?

Martin

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[chippy63]

Restriction in the system causing the pump to cycle, but if the tap is set to cold you shouldn't get any hot regardless of what the pump is doing.

Been & tried again same thing with both the shower & bathroom mixers, Rearding a restriction in the sytem would i not notice a reduction in flow
it does't pulse the flows the same just runs hot & cold when set to cold it only runs hot when set to hot.

What about the kitchen tap and is the shower a stand alone tap or is it just off the bathroom mixer tap. Has it just started doing this?

Martin

Started couple of weeks ago, Shower is seperate mixer, the kitchen tap is not affected & pump runs all the time with no hot when set to cold ?.

Karl

 

[funflair]

I think you are going to have to follow the pipes and see at what point the cold water feed to the bathroom tap for example start to feel hot/warm, that should at least tell you where the hot water is coming from, I can only guess its a back flow from the boiler or something similar but why not on the kitchen tap?

Martin

 

[chippy63]

So latest on this problem it happens with all three taps, have managed to follow some of the pipework.

So this is what i have.

Cold water from tank to shurflo pump
Cold water from pump to frost valve
frost valve then tees of to combi boiler,kitchen,shower & bathroom mixer taps cold side.

Hot water out of combi to tees to kitchen and shower mixer taps which tees of to bathroom mixer hot side.

There appears to be no non return valve should the be?.

All pipework is rigid with plastic fittings.

I really am confused why this is happening.

Karl

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[chaser]

Different system but in ours there is a non return valve actually in the fitting on the cold feed to the boiler, not immediately obvious till you take the pipe off, could easily be stuck open.

 

[hilldweller]

There appears to be no non return valve should the be?.

I really am confused why this is happening.

Karl

OK taps are feeding the cold feed only yet hot water comes out so somehow the pump is back feeding the boiler pushing hot water into the cold feed.

Or there is a venturi effect letting the cold stream such hot water out of the hot inlet.

I'm wondering if one tap has gone faulty and it's letting hot and cold to mix when off, so using come form of clamps, clamp off the water to a tap at a time, just one pipe would so and see if it stops.

 

[funflair]

So now that you have identified all the pipe work when the cold tap is open and the pump starts to run you should feel where the hot water is coming from, I guess it can only be from the boiler cold feed coming back over, and yes I would expect a one way valve.

Is there air in the boiler?

Martin

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[DBK]

It is possibly due to a fault in the temperature limiting mixer valve - if your system has one.

On our van the output from the water heater goes through such a valve. The reason is the hot water comes out at 70°C which could be potentially dangerous so it goes through a valve which mixes the hot water with cold to reduce the hot water to a safer temperature.

I guess a failed seal could cause hot water to pass into the cold side. If you have such a valve it will probably be somewhere between the water heater and the nearest hot water tap. Look for something with three pipes going into it. Ours hides under the sink behind a panel - but a different MH of course.

 

[chaser]

ours is simply a ball bearing loose in the fitting that connects to the heater.

 

[chaser]

this is all it is

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[chippy63]

OK taps are feeding the cold feed only yet hot water comes out so somehow the pump is back feeding the boiler pushing hot water into the cold feed.

Or there is a venturi effect letting the cold stream such hot water out of the hot inlet.

I'm wondering if one tap has gone faulty and it's letting hot and cold to mix when off, so using come form of clamps, clamp off the water to a tap at a time, just one pipe would so and see if it stops.

I can't really clamp a pipe off as they are all rigid, as for one tap faulty it does it at all off the taps

What is the venturi effect

So now that you have identified all the pipe work when the cold tap is open and the pump starts to run you should feel where the hot water is coming from, I guess it can only be from the boiler cold feed coming back over, and yes I would expect a one way valve.

Is there air in the boiler?

Martin

the cold water pipe does get slightly warm when the water flows hot just for a couple of seconds, you can just feel the pipe at tap end increase in temp for a few seconds.

How do i check for air in the system, i get no spluttering when running any of the taps.

Where would the one way valve be.

Karl

 

[funflair]

I think really any air and you actually have an air cushion in ALDE systems (don’t know about yours) would be a secondary issue to a non return valve issue, don’t know where though.

Martin

 

[chippy63]

Would it do any harm if i bought & ftited a non return valve, even if i already have one, Where would i put it
after the frost control valve? which is after the pump & before all the teeing off.

Karl

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[Speve]

I’m inclined to agree with @hilldweller that you have a tap that the mixer has gone capput and it’s just streaming hot water back into cold system via the tap head.
The only way to check would be to remove a tap at a time and plug it off to find which one it is.

 

[BreweryDave]

The title of the thread made me think it was something else, like....my missus, but I’m not allowed to mention it.....something to do with her age apparently....

 

[tonyidle]

I’m inclined to agree with @hilldweller that you have a tap that the mixer has gone capput and it’s just streaming hot water back into cold system via the tap head.
The only way to check would be to remove a tap at a time and plug it off to find which one it is.

Even if such a fault were possible the H & C pressures are identical (same pump) so it wouldn't cause the problem.

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[chippy63]

The title of the thread made me think it was something else, like....my missus, but I’m not allowed to mention it.....something to do with her age apparently....

Our wifes would get on well then .

Even if such a fault were possible the H & C pressures are identical (same pump) so it would cause the problem.

I'm not sure what you mean ?

 

[tonyidle]

Our wifes would get on well then .




I'm not sure what you mean ?

Edited to make sense .

 

[chippy63]

Had another feel of various pipes today, & The cold water feed to the boiler gets hot when the water in tap flows hot
Does this mean i need non return valve in the cold water feed?.

Karl

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[chaser]

Had another feel of various pipes today, & The cold water feed to the boiler gets hot when the water in tap flows hot
Does this mean i need non return valve in the cold water feed?.

Karl

why does noone take any notice of what i say just because i go for the obvious easy option.

 

[funflair]

My guess would have been YES but then I googled, dont know what your boiler is but the theory most likely holds for most,

Have a read page 18



Martin

 

[chippy63]

Boiler is a Combi 6e

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[chippy63]

why does noone take any notice of what i say just because i go for the obvious easy option.

I am hoping it is a really easy option, but not had the van that long so unsure if the elbow in the cold water feed is a non return fitting
if i take it off & its faulty i have an inline one i can put in.

Looking at the document from @funflair though it should be further down the line.

 

[hilldweller]

What is the venturi effect
Karl

What I had in mind was a T junction

PUMP>>>>>>>>>>>v>>>>>>>>>>>>cold taps
.................................... v
.................................... v
.................................... v
...................................To Boiler

So the pump pushes towards the cold taps and the T feeds the boiler
But what can happen at the junction is the water rushing across the top can suck water from the boiler not feed into it if, say an air leak in a hot tap allows this.

Clutching at straws, letting my imagination run wild.

https://en.wikipedia.org/wiki/Venturi_effect

 

[chaser]

your pump pressureises the system, it doesnt care which way it gets to your taps so its just as likely to come out of your boiler bacwards as forwards, the non reverse thing i put a link to is just a plastic ball bearing in the fitting so can wear or get stuck.

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[funflair]

Different system but in ours there is a non return valve actually in the fitting on the cold feed to the boiler, not immediately obvious till you take the pipe off, could easily be stuck open.

Doesn't that stop the frost protection valve from protecting the boiler? or do you not have one in your system.

Martin

 

[funflair]

I am hoping it is a really easy option, but not had the van that long so unsure if the elbow in the cold water feed is a non return fitting
if i take it off & its faulty i have an inline one i can put in.

Looking at the document from @funflair though it should be further down the line.

In one of your earlier post you suggest that the cold water for the taps T's off between the frost valve and the boiler, my understanding is that the T to the taps should be between the pump and the frost valve and then a one way valve can be fitted between this T and the frost valve so preventing hot water finding its way from the boiler to the cold taps.

I think what is happening is that the system is sitting under pressure in both the hot and cold side, when you open the cold tap there is an immediate drop in pressure which allows hot water to find it's way from the boiler back the wrong way up the cold pipe, when the pump starts a moment later it stops the surge but by then some hot water is on the way to the cold tap that is open, the one way valve will obviously stop this but must be the pump side of the frost valve to allow protection of the boiler from frost.

Martin

 

[Wagoneer]

This is a resurrection of an old post in July 18.

I recently had a similar problem with hot water coming out of the mixer tap when switched to the cold setting. This occurred on both the bathroom and kitchen taps.

On checking the temperature of the pipework it was noticed that hot water was getting into the cold water feed. We normally have the water temperature set to the 60C setting.

I downloaded the Truma Combi 4/6 boiler "installation instructions", out of interest. Low and behold it mentioned this exact problem. Basically, they recommend inserting a non return valve (NRV) in the cold water feed just before the dump valve.

I bought a NRV from leisureshopdirect suitable for a 10mm ID flexible pipe system. Fitting was extremely difficult in the available space but might be easier in other vans.

Initial testing seems to have cured the problem. It's a shame manufacturers don't follow the recommended installation instructions (Carthago in my case).

The following pic shows the NRV (top right).

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