When your cold water tank is full of hot water..

[RidersofRohan]

..how the hell does that happen?
We have had the van 4 weeks.
Last week while having work done on the house we lived on the drive in the Moho. We used the water heater but found that the cold tank was also being heated, seriously heated, so that we had a tank of hot water. I was told by the dealer it was a faulty non return valve. I obtained a new non return valve and fitted it, heated up the hot water for an hour or so and ran the tap hot and cold. Excellent easy solution.
So off to Lincoln Show we go.
Arrive Friday lunchtime, switch on water heater (on gas). All good so we thought.
Saturday morning our near full cold water tank is full of hot water hot enough for me to in “cold water”.

I had kept the non return valve (in picture) that I replaced so unscrewed it and looked inside expecting to find it wedged open with grit or foreign object but it looked clean and the valve seemed tight.
So I’m wondering is there a second valve somewhere else? Is it a Truma problem, it did turn itself off at one stage after it had heated the 120 litre tank. Has someone at the dealers connected the pipes up wrong?
Rapido a- class 866f, Truma heating with the Plus control unit.

 

[Lenny HB]

That type of pump doesn't need a non return valve.
Only thing I can think of that would cause a problem on the Truma is the vent valve. It's on the end of the boiler at the top it has a red collar on it, allowes air out when the boiler is filling. Normally when they go faulty water flows out the vent pipe which goes out under the van.
Can't really see what is causing it unless something seriously wrong with the plumbing install.

 

[Landy Andy]

Assume you don’t have a tank heater for cold climates, and have it on by accident

 

[Langtoftlad]

Do you have tank heaters [to be used in freezing weather]?
Are you accidently switching them on perhaps.
How warm is the grey water?

 

[Jimbohorlicks]

I think the waste and cold tank heaters are usually electric and are not gas operated.
Were you on ehu at Lincoln?

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[Langtoftlad]

I think the waste and cold tank heaters are usually electric and are not gas operated.
Were you on ehu at Lincoln?

They are electric but run off the leisure battery...
T'was just an idea

 

[RidersofRohan]

That type of pump doesn't need a non return valve.
Only thing I can think of that would cause a problem on the Truma is the vent valve. It's on the end of the boiler at the top it has a red collar on it, allowes air out when the boiler is filling. Normally when they go faulty water flows out the vent pipe which goes out under the van.
Can't really see what is causing it unless something seriously wrong with the plumbing install.

Thanks.
The Truma is hidden under the sink, I will try to remove more bits to get a view of it.

 

[RidersofRohan]

Assume you don’t have a tank heater for cold climates, and have it on by accident

I don’t think this model has a tank heater, no idea where a switch would be. But we are talking serious heat here, the cold water is as hot as the hot water, no tank heater could achieve that with 100+ litres of cold water.
Can’t use the shower today the water is just too hot.

 

[RidersofRohan]

I think the waste and cold tank heaters are usually electric and are not gas operated.
Were you on ehu at Lincoln?

No relying on gas, luckily I filled both gas tanks up on our way here. Used nearly a full tank since Friday. Turned all heating off the van is like an oven.

 

[RidersofRohan]

The boiler.
It means nothing to me.
Not surprisingly the top of the boiler is really hot, the other pipes have cooled as the boiler has been off for 40 minutes.

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[Lenny HB]

The boiler.
It means nothing to me.
Not surprisingly the top of the boiler is really hot, the other pipes have cooled as the boiler has been off for 40 minutes.View attachment 669170View attachment 669171

The red thingy on the left is the vent valve (they were white with a red collar).

Just found this in the install manual.

 

[68c]

So is this saying once the pump reaches pressure and switches off, the heated water from the heater tank flows back by gravity to the main/cold water tank. (Assuming it has a main tank lower than the heater tank). If the pressure in the system drops the pump restarts sending the now luke warm water from the main tank to the heater tank, repeating this over a time raises the temperature in the main tank. Fitting the non return valve prevents this. What I do not understand is how the heated water flows backwards through the pump unless its own non return valve is faulty which would be indicated by frequent pump running even when no taps are used.

 

[RidersofRohan]

Many thanks.
Lenny I think that is what I have. The NRV is after the pump and before the Frost Control.
68c, The Truma and the tank are next to each other at the same level. The odd thing is the pump hasn’t been running excessively, and it is loud so we would have heard it. I switch it off at night and sometimes when we go out. The pump is very hot to touch, so hot water is presumably running through it, although it’s position above the cold tank could mean that it’s picking its heat up from the “no longer cold“ tank. It’s weird.

 

[Lenny HB]

The pump shouldn't be hot unless it's been running a lot. Water should not be able to back feed through that type of pump unless the pump is faulty.
Providing there are no leaks in the system the pump shouldn't run unless there is a tap open.

 

[Landy Andy]

How much pipe work can you get to? On domestic plumbing sometime a tap valve cartridge can allow reverse flow through it. I’ve found it mostly with shower valves. It is easily cured by fitting a NRV on the cold supply. Can you get to where the cold water system splits between supply to boiler and cold supply?
or fit the NRV after pump, and before anything is piped from it

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[RidersofRohan]

How much pipe work can you get to? On domestic plumbing sometime a tap valve cartridge can allow reverse flow through it. I’ve found it mostly with shower valves. It is easily cured by fitting a NRV on the cold supply. Can you get to where the cold water system splits between supply to boiler and cold supply?
or fit the NRV after pump, and before anything is piped from it

We have a leaky bathroom tap, we are waiting for the tap to be available. Are you saying the hot could be pushing back the cold water within the tap and a reverse flow back to the cold tank?
Would that require the flow to force its way past the NRV. and through the pump, and without the pump running?
The truma has been off since this morning and both hot and cold pipes underneath the bathroom tap are now cold. Suppose I set the water heater running and then see if both pipes heat up would that prove your theory?

 

[Gellyneck]

We have a leaky bathroom tap, we are waiting for the tap to be available.

Probably the least of your worries just now and nothing to do with your hot water problem but could the leak in your tap be fixed by replacing the ceramic mixer cartridge (obviously if it has one!).

 

[Lenny HB]

If you look at that Truma diagram your non-return valve is in the wrong place.
As your plumbing is flexible pipe you could try clamping the pipe off by the faulty tap.

 

[RidersofRohan]

Not sure where the NRV should be as I can’t find the pipes heading out from this picture. The top pipe I assume is the overflow. The right hand blue pipe I assume comes from the tank but literally disappears downward the other side of the seat back. The left hand where the NRV is becomes a black pipe as it goes through the seat back and that too heads downward to some place where even my girlie type hands ( never done a days manual labour in my life) cannot go.
Under the sink at the other side of the seat belt anchors is the Truma with numerous black and blue pipes none appear to come from under the seat.
I’m totally lost it’s way beyond me.
Think I will hope Spinneys solve it without too many trips to Cheshire. Thanks to everyone who have contributed and when it is resolved I will update this thread so anyone else in this predicament has a starter.

 

[gus-lopez]

..how the hell does that happen?
We have had the van 4 weeks.
Last week while having work done on the house we lived on the drive in the Moho. We used the water heater but found that the cold tank was also being heated, seriously heated, so that we had a tank of hot water. I was told by the dealer it was a faulty non return valve. I obtained a new non return valve and fitted it, heated up the hot water for an hour or so and ran the tap hot and cold. Excellent easy solution.
So off to Lincoln Show we go.
Arrive Friday lunchtime, switch on water heater (on gas). All good so we thought.
Saturday morning our near full cold water tank is full of hot water hot enough for me to in “cold water”.
View attachment 669110
I had kept the non return valve (in picture) that I replaced so unscrewed it and looked inside expecting to find it wedged open with grit or foreign object but it looked clean and the valve seemed tight.
So I’m wondering is there a second valve somewhere else? Is it a Truma problem, it did turn itself off at one stage after it had heated the 120 litre tank. Has someone at the dealers connected the pipes up wrong?
Rapido a- class 866f, Truma heating with the Plus control unit.

Could it be the same as Karl Gromett did the other day & shut off the shower using the hand held valve but had left open the actual mixer valve so that the hot could be pumped through the cold pipes continually?

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[Lenny HB]

You could try fitting a no-return valve in the cold supply to the boiler just before the boiler.

 

[Landy Andy]

Are you saying the hot could be pushing back the cold water within the tap and a reverse flow back to the cold tank

Yes. That is what I’m saying. The hot system joins the cold, and if the valve is letting water pass.

if your cold water tank is getting hot, then somewhere water is flowing backward

 

[gus-lopez]

Yes. That is what I’m saying. The hot system joins the cold, and if the valve is letting water pass.

if your cold water tank is getting hot, then somewhere water is flowing backward

& as Karl found out the only place they join is at the mixer tap for the shower usually.

 

[RidersofRohan]

Well if the answer is to fix the leaky tap then I should be well pleased.
I still don’t understand how the hot gets all the way back to the cold tank, but I can see the plausibility of the mixer tap mixing up the hot and cold having now read Grommets thread.
Tomorrow will be a phone call to chase up the tap.
Thanks everyone it felt more serious than the leaky tap so I I concentrated on the hot tank issue and left the leaky tap leaking into cloths while the sneaky leaker was the real cause of my problem.

 

[Landy Andy]

can you reach the cold pipe supply to the tap? If so is it getting hot whilst tap is off?

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[Minxy]

Well if the answer is to fix the leaky tap then I should be well pleased.
I still don’t understand how the hot gets all the way back to the cold tank, but I can see the plausibility of the mixer tap mixing up the hot and cold having now read Grommets thread.
Tomorrow will be a phone call to chase up the tap.
Thanks everyone it felt more serious than the leaky tap so I I concentrated on the hot tank issue and left the leaky tap leaking into cloths while the sneaky leaker was the real cause of my problem.

What's the tap you're after?

 

[RidersofRohan]

What's the tap you're after?

The dealer was supposed to be sourcing one last Tuesday, but I have had a message to contact them on Monday. I am hoping this is a free fit as I have only had the van 4 weeks.

 

[Landy Andy]

Are you keeping the dodgy tap with the tap lever in the mid position? Possibly, and I mean possibly, if you put the lever, to adjust the temp, one side (hot or cold) it MAY stop this happening.

 

[RidersofRohan]

can you reach the cold pipe supply to the tap? If so is it getting hot whilst tap is off?

The water heater and water pump haven’t been on since this morning, we are going home tomorrow so trying to do without it.
However both pipes were hot this morning. ( along with every other water pipe, tank etc).

 

[Gromett]

Could it be the same as Karl Gromett did the other day & shut off the shower using the hand held valve but had left open the actual mixer valve so that the hot could be pumped through the cold pipes continually?

No that is a different problem.

In my self builds there are in fact 2 non return valves. The first is built into the pump (depends on which pump you are using) This is to stop water returning to the tank.

I ALSO fit a non return valve just before the heater dump valve. This is to prevent warm water getting back into the cold system.

If you are getting warm water in your cold tank, then it suggests that there isn't a non return valve just before the hot water boiler AND/OR the one near the pump is non functional.

You can test a non return valve by blowing in it.

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