CW tank overflowing randomly for approx 20 mins daily.

[Bennychad]

Hi Folks.
I have a property where at random times daily the cw tank expels water for a 15-20 mins from the pipe at the eaves.
I felt warm (not hot) water feeding into the tank from the pipe that feeds the H/W cylinder.
It didn’t have a lot of pressure but when I blocked it with my finger water came in from the vent pipe in cw tank lid.
Ive done everything listed below and as it’s random I have to wait to see if the problem returns.
(Mains cold / cylinder fed hot mixer taps)
I have fitted a non return valve to hot feed at kitchen sink tap.
Isolated 3 bathroom mixer taps on different days as these were mains cold.

Problem still here unfortunately.
Today I’ve replaced the cylinder thermostat but think the old one was actually ok as it shut the boiler off when I reduced the temp setting.

I’m stuck with this one.
No issues with the F&E tank that I know of.

Any ideas?
Thanks.

 

[Johntheo5]

How is the shower fed?.
Is there a electric immersion timed to come on daily?.

 

[Bennychad]

Hi there.
There is no immersion in this cylinder.
Thanks
Ben

 

[Bennychad]

How is the shower fed?.
Is there an electric immersion timed to come on daily?.

Sorry. The shower is fed balanced from the cylinder and cw tank

 

[Johntheo5]

Can/have you isolate the cold to the balancing valve?

 

[Bennychad]

Can/have you isolate the cold to the balancing valve?

I haven’t as it’s not mains fed so didn’t think it could push water up to the tank

 

[Johntheo5]

Thats correct, when I saw balanced I thought (wrongly) mains cold. It does point to one of the 3 mixer valves despite isolating them. Is the F&E tank mounted above the CWST, if it was then a leaking cylinder coil would cause the CWST to overflow but this would be continuous and the F&E tank would be making up continuously. If no F&E tank problem then maybe install NRVs (if possible) on all three mixers?.

 

[JohnD]

(Mains cold / cylinder fed hot mixer taps)
.

Feel the pipes under each of the mixers. When you have not used them for a while they should both be at room temperature. The one that is leaking internally will be cold due to water from the main passing through it.

Very likely a shower mixer that is old or the cheap bar type, or a joystick type sink mixer.

Do you have isolating valves under all the taps?

Tie up the ball floats in the cold water cistern, and the CH feed and expansion.

 

[Bennychad]

Thats correct, when I saw balanced I thought (wrongly) mains cold. It does point to one of the 3 mixer valves despite isolating them. Is the F&E tank mounted above the CWST, if it was then a leaking cylinder coil would cause the CWST to overflow but this would be continuous and the F&E tank would be making up continuously. If no F&E tank problem then maybe install NRVs (if possible) on all three mixers?.

F&E tank is next to the CWST water level in F&E well below level of CWST tank.
No issues with the F&E outlet as always CW outlet that expels water - it runs like a hose pipe for around 20 mins randomly.

I have 4 x mixer taps;
Kitchen - NRV installed on hot side
3 x bathrooms - iso valves fitted to 2 of them and one capped off at the moment.
Ive isolated them on different days so there was no chance of mains cold passing and the problem still occurred.

There is a mixer on the shower and the bath but both are gravity fed from not/cold tanks

Its baffling me and also plumbers who are advising me.

Thanks

 

[Bennychad]

Feel the pipes under each of the mixers. When you have not used them for a while they should both be at room temperature. The one that is leaking internally will be cold due to water from the main passing through it.

Very likely a shower mixer that is old or the cheap bar type, or a joystick type sink mixer.

Do you have isolating valves under all the taps?

Tie up the ball floats in the cold water cistern, and the CH feed and expansion.

Thanks for the reply - does the answer above cover what you'd covered...
Cheers

 

[Johntheo5]

I would run them as JohnD suggested run each on hot only then shut off and see if hot pipe cools down or not. The 20 minute daily period is strange though.

 

[Johntheo5]

A long shot, washing machine with hot&cold fill??.

 

[Bennychad]

A long shot, washing machine with hot&cold fill??.

Cold fill only on the washer. thanks

 

[Bennychad]

Im now told by my tenant that prior to this happening - there is a bumping/banging noise coming from the pipes around teh cupboard where the cylinder is.

 

[JohnD]

Are you sure there is no immersion heater?

Look again.