Water overflowing into header tank - but from where ?

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My electric only house immersion heater blew and I wanted to replace it with an instant water heater. So I plumbed it in, as I have done in a few other properties without incident, and it was fine for a couple of days.

However, today, an overflow / expansion vent from the old immersion heater suddenly started dripping water into the header tank. This seemed impossible as the immersion tank is not now used. The cold water is off the mains and the hot water is off the mains. Yet there must be some plumbing I cannot see (it is an old house).

I'm guessing a valve near the (stand alone) shower ? pressure value somewhere ? I read something about mixer taps causing problems but I cannot isolate it.

What I have found it that something is drawing water through the water heater, which is off the cold water main, even when all taps and showers are turned off.

But whatever it is was not doing this until today.

Any ideas ?

Canucklehead

Hi,

One of those problems that can only be answered by being there in front of it.




GSR.

karl-123

bad plumbing somewhere,like you say possibly a mixer tap bypassing or shower,
when the hot feed comes out of the cylinder top it , tees off, to above for expansion and below for hot feed,
did you cap this off properly when switching over to mains,

gate valves are not designed for use on the mains, they will pass mains cold water,

property.advert

Canucklehead wrote: »

Hi,

One of those problems that can only be answered by being there in front of it.

GSR.

I know, almost impossible to describe accurately without posting a mini War and Peace !

Googling around, I came up with this Q&A from Bristan: http://www.bristan.com/Customer-Service/Troubleshooting

Question:

Water is coming from the cold water tank overflow pipe, and there is warm water in the tank

Answer:

Hot water is flowing from the shower, up the cold water pipe and into the tank. Check the non-return valves on the shower, or fit an in-line non-return valve in the cold water shower supply pipe to stop the problem.

This describes the symptoms but seems impossible as the cold inlet feeds the water heater, which then does not seem to have a return route to this overflow / vent. Yet water is flowing through the new heater but not backwards, which a non return valve would solve.

I am assuming it is connected with the change in the pressure the old immersion being fed from a header tank and the new heater being fed from the mains. However, with the cold also fed from the mains, there should be equilibrium.

On the subject of non return / check valves, just where to put them, if necessary ? The net seems to have all manner of conflicting advice: next to hot tap, on cold supply etc.

ormus

you can put NRVs anywhere convenient on the H/C pipes.
as near the device as possible. and before any service valve.
ie
the ones on my shower are just behind the false wall, behind the shower mixer.

keystone

I agree with CH - need to understand where and how you have plumbed in your water heater and where and how you have isolated the hot water cylinder containing the (duff) immersion heater. Whilst what the Bristan article says is true it assumes that its piped conventionally. You may have left a pipe in place that you shouldn't have. Just fitting no-return valves willy-nilly won't help unless you understand how its piped.

Though of posting some pics? One or two are worth a W&P epistle any day. But make them so that we can actually see how its piped.

Cheers

property.advert

Is there anywhere I shouldn't put NRVs ? such as before a heater.

I've a mixer tap and have read they should be as near as possible to the taps.

As for the shower, I can't access it without ripping half the bathroom apart so can I just add another one, where I can gain access, on the possible assumption that one previously working has failed ?

property.advert

keystone wrote: »

I agree with CH - need to understand where and how you have plumbed in your water heater and where and how you have isolated the hot water cylinder containing the (duff) immersion heater. Whilst what the Bristan article says is true it assumes that its piped conventionally. You may have left a pipe in place that you shouldn't have. Just fitting no-return valves willy-nilly won't help unless you understand how its piped.

Though of posting some pics? One or two are worth a W&P epistle any day. But make them so that we can actually see how its piped.

Cheers

Only a minimum of pipework is visible but I'l try to get something visual.

keystone

OK thanks. That might be your problem if you misidentified a particular pipe during your modification.

Logically if you didn't have this problem before but you do now that you have altered the system then its something that you have done in respect of piping it. Not wishing to be rude but you need to trace what does what. So CH answer is still correct as if you can't trace and understand the pipework yourself you'll need to get someone with knowledge in to look at it for you.

Cheers

ormus

i wasnt suggesting to go ahead and fit the NRVs willy nilly. just answering the OP question.

last line, post 4.

keystone

ormus wrote: »

i wasnt suggesting to go ahead and fit the NRVs willy nilly. just answering the OP question.

last line, post 4.

No you misunderstand. My comment was directed at the OP and

....can I just add another one, where I can gain access, on the possible assumption that one previously working has failed..

kinda suggests I was right to make the comment.

Cheers