Header Tank Overflowing with Warm Water

[stewartacraig]

Okay, I saw a couple of threads about this issue before, but I think my problem may be slightly different...

I have an open-vented hot water cylinder with a cold water feed and expansion tank in the loft which keeps overflowing whether the hot water/central heating is on or off. When I put my hand into the feed and expansion tank I can feel warm water is being forced back up the pipe which I assume is meant to feed cold water down into the hot water cylinder. The only way I can stop the overflow is by turning off the mains cold water supply to the house!

Things I have checked already...

Central heating is working fine. All radiators are full with no air in the system.
Thermostat on hot water cylinder works fine. When I adjust the temp down the hot water clicks off.
Ball Valve in the feed and expansion tank is working correctly. It's not leaking cold water into the tank.

Is it possible that the mains cold water fed into the system is forcing its way through a split coil in the hot water cylinder causing this to completely fill and force water back up into the feed and expansion tank? Or maybe there is some other explanation for this?

Any thoughts/ideas would be greatly appreciated.

Cheers,
Stew

 

[ajs heating]

>Is it possible that the mains cold water fed into the system

mains water does not feed the system in any way it's a gravity fed system.

>force water back up into the feed and expansion tank.

is it going up to the f/e tank or cws tank ?

if you have a split coil in the cylinder check the other tank if one is filling the other willbe emptying and the ball valve willbe letting in to fill the emptying tank.

which tank is the highest cws or f/e ?


by the sounds of it you have either a shower mixer or a mixer tap that is cold mains and gravity hot and the non return valve is faulty and passing cold to the hot.

 

[Phil]

If you find out what is causing it 'Stewartacraig' then do tell, I would be interested to know.

 

[stewartacraig]

Thanks for your reply, AJS Heating, and for clarifying the point about the cold water feed...

There are two tanks in the loft which I may have confused... A little one which appears to be fine (perhaps this is what is called the F/E tank?). Then there is a much larger tank connected to the hot water cylinder (perhaps this is the CWS (cold water storage?) which is the one that keeps overflowing. The base of both tanks sit on the same wooden supports so they're both the same height.

I do have a mixer tap in the kitchen and one in the bathroom and a thermostatic mixer shower which are all cold mains and gravity hot so I guess I need to inspect each of these for a non-return valve issue. Not sure how I'll know if they're working correctly though... Any ideas how I can test this?

 

[ajs heating]

as you say your tanks are both on same platform but useally cause your cws holds more water the level will be higher than the f/e.
and this is not being affected so it must be an issue with a mixer etc.

my first check would be the shower mixer. check along the hot/cold pipes to the shower from the supply and look for any isolation valves and if so shut them off.
if it stops overflowing thats the problem mixer if not move on to the next tap etc.


what shower mixer have you ?
is it an old install ?
as many now will not work on mixed pressures only balanced pressure.
i take it its not a thermostic mixer valve.

 

[stewartacraig]

Sure, the water in the CWS is much higher than the f/e.

Okay. I will isolate both hot and cold feeds to the shower tonight and put the cold mains feed to the house back on. As you say, if the cws doesn't start to fill up again, it must be that. The shower is a thermostatic mixer and it's only around 3 years old so I didn't think this would be the problem, but I'll definitely check it out, and do the same for the other two mixer taps.

One other thing you reminded me about when talking about balancing the pressure, I did fit a valve on the cold feed into the house that allows you to adjust down the pressure of the cold water. I did this to try and balance the cold and hot feeds a bit better to help the operation of the thermostatic mixer shower. Maybe I should try and tweak that a little to drop the cold feed pressure...?

Will post back tonight on what I find out anyway...

Cheers!
Stew

 

[ajs heating]

if you have fitted a prv on the cold mains i would say its set abit high still as it is over powering the hot.
you could have fitted it to just the shower supply as fitting it to the mains inlet to the whole house can drop the pressure on certain things that you don't want dropped like your tank ball valves, garden tap, etc.

 

[stewartacraig]

I hindsight, I should have fitted the PRV just to the cold feed to the shower. I'll check this out first anyway and try and drop the pressure down to see if this resolves the problem. If not, then I'll move on to isolate the shower mixer itself and then each of the tap mixers to see if this works.

Appreciate the advice. I'll check this all out tonight and post back what I find out...

if you have fitted a prv on the cold mains i would say its set abit high still as it is over powering the hot.
you could have fitted it to just the shower supply as fitting it to the mains inlet to the whole house can drop the pressure on certain things that you don't want dropped like your tank ball valves, garden tap, etc.

I think you were right, AJS Heating. I tried kind of what you said, but a little different... In addition to the isolators on the mixer tap in the bathroom and the isolators on the mixer on the shower I also have isolators for the whole of the bathroom. I switched both the bathroom isolators off and the CWS tank ceased to fill up...

Then I just switched the cold isolator on so that I should only get cold water out of the sink mixer tap in the cold position and nothing when I move the tap round to the hot position, but I get cold feed water coming out when the sink mixer tap is in the hot position, so the cold feed water must be going into the shower mixer and coming back round through the supposedly non-return hot valve and out of the tap when it's in the hot position...

Looks like it's going to be a difficult job to get the hot non-return valve out to have a look at it and even then I'm not sure what I'll be able to do with it if I do get it out... Any ideas?

Cheers,
Stew

 

[ajs heating]

buy a couple of non return valves (check valves) and fit them to the hot supply to the shower and basin tap.
that will stop the cold passing back to the hot.
saves pulling all the shower mixer apart.

 

[stewartacraig]

Cheers, AJS Heating!

Will do that at the weekend and post back, hopefully, when it's all sorted...