Overflow head scratcher !

[Gez2312]

Hi, been to a customers house tonight .

Overflow running from domestic tank , took a ball tap - thought I already knew the problem!

Ball tap tap is working fine , submersed under water

ran some hot water off , level in tank dropped .

Bent arm arm down on ball tap , it shut off around 3" below overflow (cylinder was hot)

Checked cylinder stay and zone valve operation.

Heating system is sealed, and is holding pressure so think coil is not split

water in in header tank is tepid , and cold fill pipe to cylinder (a floor below) is warm

nothing from expansion , if it was back flow from somewhere surely it would come over expansion , not push water in cylinder up feed pipe?

Sctraching my my head now, maybe just missing something simple ! Any ideas gratefully received , I used to think I was quite clever !

 

[oily face]

Your mains is more than likely back feeding somewhere. .last time i had one of these over flow mystery it was a dodgy kitchen mixer tap sending the main water up the hot

 

[jonnyswamp]

Is there an unbalanced mixer tap/shower somewhere that hasn't got non return valves fitted, could be passing back up hot dist pipe

edit
posted same time as oily, didn't copy honest

 

[Gez2312]

But surely in would run out of expansion pipe rather than into cylinder and lift the weight of water up the cold feed ?

I've had the dodgy kitchen tap scenario on a combi before, that had , had everything relplaced for poor hot water first !

If it was a steady run from expansion I could understand it ! But I'm head scratching at this one!

Customer says only difference to usual is hot water has been on constant rather than timed due to guest staying

 

[gassafe]

Maybe that guest is using a bathroom or shower that has not been used for ages / faulty shower mixer?

 

[Gez2312]

Yeah that could be the case , bloody trouble causing guests!

But why hot water back up feed pipe and not just cold running from expansion ?

 

[Best]

It will come up the feed pipe into the tank. Seen this before. You can watch the haze in the water if you shine a torch on the bottom connection inside the tank.
Usually a monobloc tap is the culprit I find

 

[Unregistered]

Will have to go and investigate further but it's quite and old fashioned house , and from what I can remember all taps are either separate or old school full turn type mixers, not these modern ceramic mixer ****e !j

 

[Gez2312]

Will have to go and investigate further but it's quite and old fashioned house , and from what I can remember all taps are either separate or old school full turn type mixers, not these modern ceramic mixer :nono: !

 

[missplumb]

the water in the system will rise uniformly up the cold feed and the vent pipe, but it will reach the the water level in the cwsc before it will go over the top of the vent hence why its not coming out of the vent!

 

[gassafe]

Bung the cold feed temporarily if you want to watch it come over the vent!

 

[Sparkgap]

First thing I'd look for is to check mixing valves for stuck check valves, only takes a slight weep through if you've got mains on one side and tank on the other. As for overflow coming up expansion pipe, won't happen unless you've got a lot of pressure blasting it up! :smile5: