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

Gromett said:
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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Now I am confused.
Here is a picture of the heater and cold water dump valves bottom right. The Truma unit is at the top of picture and the cold tank to the right.
C4400E61-0BD8-4A93-BAF3-125DD4FB4C49.jpeg

I have blown through the NRV that I have taken out and no air travels in the wrong direction, so it didn’t fail it just didn’t help? Similarly it’s replacement isnt failing either.
Presumably putting it in the pipe heading to the Truma from the light blue drop valve to allow only flow in the direction of the Truma unit is what is needed?
Thanks again.
 
Just an observation which is probably not relevant but ... the bottom grey lever should sit parallel with the pipe the same as the red one, not angled to the side.
 
Minxy said:
Just an observation which is probably not relevant but ... the bottom grey lever should sit parallel with the pipe the same as the red one, not angled to the side.
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That could be relavent as its a drain valve it could be letting air, they did say the pump was running ocassionly. Only takes a minute air leak to upset a pressure switched system.
Also there have been leaks around that area just look at the state of the floor.
 
Lenny HB said:
That could be relavent as its a drain valve it could be letting air, they did say the pump was running ocassionly. Only takes a minute air leak to upset a pressure switched system.
Also there have been leaks around that area just look at the state of the floor.
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The pump hasn’t been running outside of what might be considered normal. It’s loud so we would have noticed.
No idea if there have been leaks there before as we have had the van 4 weeks. It’s dry there now, no wonder the amount of heat in that area!

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Ok home from Lincoln. Message from dealer was they had sourced the tap. However when I rang up the earliest they could do it was 3 Nov. Taking the pee.
So I replaced the cartridge, easier than I expected. But still leaking.
Surely the cartridge bit is where the hot meets the cold, if that wasn‘t leaking then does the theory that the water tank was heated by back flow of water down the cold supply get blown out of the water?
 
Fit a NRV immediately after the pump. On the pipe before it splits. The hot water MUST be going into the water tank, and I assume you like most only have one outlet for water.
 
Landy Andy said:
Fit a NRV immediately after the pump. On the pipe before it splits. The hot water MUST be going into the water tank, and I assume you like most only have one outlet for water.
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There is already one there, I think it needs to be on the cold fill to the boiler.
 
Lenny HB said:
There is already one there, I think it needs to be on the cold fill to the boiler.
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I agree, on ours I fitted an outside tap and a manual switch for the pump.

Sometimes I fill the dog bowl without switching on the pump. It always runs hot from the back flow from the Truma tank if the pump is off. Never an issue with the taps as they are under pressure as the pump switches on.

It’s a simple and easy fix just to eliminate that theory.
 
There can’t be a working one, as the water in the tank is hot, so must be returning from the boiler to the tank. There is one pipe leaving the tank, and if a NRV is fitted to it before anything branches off it, then nothing can return to the tank.

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If there is one fitted how can hot water enter the tank?

i think the fitted NRV is after the cold system has been T‘d off the main.

Put a NRV where the red mark is. Then nothing can enter your water tank. Be that via hot system, or cold system.
A0F21F79-07C0-4063-AD35-52959B32B163.jpeg
 
Landy Andy said:
If there is one fitted how can hot water enter the tank?

i think the fitted NRV is after the cold system has been T‘d off the main.

Put a NRV where the red mark is. Then nothing can enter your water tank. Be that via hot system, or cold system.
View attachment 670104
Click to expand...
The OP's first photo shows one imedetly after the pump as I said it doesn't need one there as those pumps can't back feed.
Truma recommend fitting one just before the dump valve which is just before the cold feed to the boiler which is what I said.
Screenshot_2022-09-26-21-34-20-78_3aea4af51f236e4932235fdada7d1643.jpg
 
Landy Andy said:
If there is one fitted how can hot water enter the tank?

i think the fitted NRV is after the cold system has been T‘d off the main.

Put a NRV where the red mark is. Then nothing can enter your water tank. Be that via hot system, or cold system.
View attachment 670104
Click to expand...
Thanks Andy.
But isn’t that where the NRV is on my photo here: after the pump and before anything else. The NRV is the new one I fitted last week replacing one that I couldn’t find anything wrong with when I took it out.
A66EA8B0-F3B7-47C0-9F1A-A4AE85BFA98F.jpeg
 
Is the frost control valve the black box shape in the left hand corner of this photo? If so should I put the spare NRV I now have into the pipe heading towards the left side of the photo? It feels wrong to me as surely the the water in the boiler needs to outflow if the temperature drops to near freezing but the NRV will stop flow in that direction.
D5412720-8FC8-4825-B5CF-B6EC799171F9.jpeg
 
My two pennorth for what it's worth. If the blue pipe in your pic is the only one going into the tank then that is where the hot water is getting in. Therefore it has to be back feeding through the pump. Have you checked all round the tank to make sure that there isn't another pipe feeding into the tank, possibly from an over pressure valve somewhere else in the system. As I said, if there is no other connecting pipe into the tank, it must be through the pump.

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RidersofRohan said:
Is the frost control valve the black box shape in the left hand corner of this photo? If so should I put the spare NRV I now have into the pipe heading towards the left side of the photo? It feels wrong to me as surely the the water in the boiler needs to outflow if the temperature drops to near freezing but the NRV will stop flow in that direction.View attachment 670114
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That's why Truma say to put it on the other side of the dump valve
 
Lenny HB said:
The OP's first photo shows one imedetly after the pump as I said it doesn't need one there as those pumps can't back feed.
Truma recommend fitting one just before the dump valve which is just before the cold feed to the boiler which is what I said.
View attachment 670109
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Between nos 27 and 25?
 
TheTwoOfUs said:
My two pennorth for what it's worth. If the blue pipe in your pic is the only one going into the tank then that is where the hot water is getting in. Therefore it has to be back feeding through the pump. Have you checked all round the tank to make sure that there isn't another pipe feeding into the tank, possibly from an over pressure valve somewhere else in the system. As I said, if there is no other connecting pipe into the tank, it must be through the pump.
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Thanks I like your logic but I’m struggling to get to places where the pipes disappear to. This morning I started dismantling the seat, however it is well built and I think I would need to dismantle the entire seating unit. I stopped at that point.
My next idea is to empty the tank and video the interior of the tank to check for pipe entries. I might then be able to get to wherever they are on the outside of the tank by perhaps removing a kitchen drawer rather than the seating area.
The Truma unit is up on stilts with pipes going underneath it. From looking at the Truma booklet the pipe under the “a” of the Truma label is the cold water entry point from the tank, the black pipe then disappears under the unit presumably is the same black pipe in my early picture of the tank, pump and NRV.8E149AE1-F76D-47F4-BD92-3544C9C14863.jpeg
 
Just a thought, have you looked under the van to see if the dump and drain valves have pipes that are open to air, rather than connected to each other, just in case somebody has bodged a leaky valve by joining it to another pipe.
Another thought, is the vent pipe from the boiler (the one with the red valve on it) going through the floor to discharge or does it vent into the cold tank ?
Both unlikely, but worth checking.

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If the tank is getting filled with hot from the boiler how is the boiler getting replenished without the pump being active to circulate it.
Even if the pump was allowing a backflow it would be so small it would be cooled instantly by the volume (70 to 100litres) of the cold fresh tank
 
I wonder if a previous owner liked long hot showers so wired up the fresh water tank so it could be heated up .... okay I'll ... :getmecoat:
 
Minxy said:
I wonder if a previous owner liked long hot showers so wired up the fresh water tank so it could be heated up .... okay I'll ... :getmecoat:
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That's as possible as any other theory

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RidersofRohan said:
.
View attachment 669110
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In this first photo you can see the pump with the feed to it on the left & outlet from the pump on the right . So what is the blue pipe on the left doing? is it a vent pipe? I fail to see how water can be returning to the cold tank ? there should be no pipework from the tank except the inlet to the pump:
 
gus-lopez said:
In this first photo you can see the pump with the feed to it on the left & outlet from the pump on the right . So what is the blue pipe on the left doing? is it a vent pipe? I fail to see how water can be returning to the cold tank ? there should be no pipework from the tank except the inlet to the pump:
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I think the top blue pipe is an overflow / air escape pipe. It goes from the very top of the tank.
I have found another pipe, see picture from within the tank. It is part way up the tank wall and I think this may be to empty the tank to 20% water level for travelling. I haven’t found where this goes to yet. I haven’t had time today to pursue the search. Hopefully will do tomorrow.D9FFB5BA-D149-46E3-8435-E159ABEA3FFC.jpeg
 
Without seeing the other end of the blue pipe it's not obvious, but the most likely purpose of it is that it's the filler inlet, given that it appears to enter at the top of the tank.
In my experience, mixer valves are nearly always the cause of backfeeding, especially with presurised systems like combi boilers, which is why Water Regs for dwellings require them to be fitted. The fact that few people, professional or amateur, read them, is beside the point. At the minimum, fit one on every cold inlet, or at least as previously suggested before the first tee after the outlet from the cold tank.
 
chrish said:
Just a thought, have you looked under the van to see if the dump and drain valves have pipes that are open to air, rather than connected to each other, just in case somebody has bodged a leaky valve by joining it to another pipe.
Another thought, is the vent pipe from the boiler (the one with the red valve on it) going through the floor to discharge or does it vent into the cold tank ?
Both unlikely, but worth checking.
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Yes the drain valves drain to the outside, I have located those and drained the tank.
Not sure where the red valve on the Truma goes to..
 
Minxy said:
I wonder if a previous owner liked long hot showers so wired up the fresh water tank so it could be heated up .... okay I'll ... :getmecoat:
Click to expand...
Well it doesn’t work, on Saturday the water in the cold tank was so hot you couldn’t shower in it.

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