CWSC overflow problem

[pg1066]

I have an intermittent problem with the CWSC (cold water storage cistern) in the loft overflowing.

Today I saw a slight flow of water into the CWSC from the DHW cold feed, picked out by the torch when I was looking in the CWSC, evidently the temperature difference made the flow visible.
The DHW cold feed was slightly warm.
The DHW outlet from the cylinder was cold. When I opened a hot tap the DHW outlet quickly warmed up, the water being quite warm rather than hot.
The overflow rate is a steady trickle.
The heating system had been off for several hours, the pipes at the boiler were cold. The immersion heater was off.
The heating system f&e tank is above the level of the CWSC but does not appear to be losing and replacing water. A plumber has advised that the coil in the cylinder is not leaking.
The DHW cylinder is indirect, gravity fed from a gas boiler.

It would appear to me that water is flowing back through the DHW system into the top of the DHW cylinder pushing the hot water down enough for warm water to flow back up into the CWSC. This is not due to expansion as it does not occur due to the water being heated.

Any suggestions please.

[summy]

I have an intermittent problem with the CWSC (cold water storage cistern) in the loft overflowing.

Today I saw a slight flow of water into the CWSC from the DHW cold feed, picked out by the torch when I was looking in the CWSC, evidently the temperature difference made the flow visible.
The DHW cold feed was slightly warm.
The DHW outlet from the cylinder was cold. When I opened a hot tap the DHW outlet quickly warmed up, the water being quite warm rather than hot.
The overflow rate is a steady trickle.
The heating system had been off for several hours, the pipes at the boiler were cold. The immersion heater was off.
The heating system f&e tank is above the level of the CWSC but does not appear to be losing and replacing water. A plumber has advised that the coil in the cylinder is not leaking.
The DHW cylinder is indirect, gravity fed from a gas boiler.

It would appear to me that water is flowing back through the DHW system into the top of the DHW cylinder pushing the hot water down enough for warm water to flow back up into the CWSC. This is not due to expansion as it does not occur due to the water being heated.

Any suggestions please.

its possible for cold water to push back thru mixer taps or thermostatic showers , have you any of these

[pg1066]

Bath mixer tap with shower fed from CWSC.
No mixers on unbalanced supply.

[summy]

so the bath on the cold side is fed from cws tank not the mains

[pg1066]

Yes, only tap on mains is kitchen cold tap which is not a mixer tap.

[Puddle]

Well you say intermittent,when does over flow drip

If backing up cold feed to cylinder seems would be cold mains as all bathroom on tank,should be ok
Take it cylinder expansion pipe over cylinder clear of tank water line
Taps in kitchen separate so that should be ok
We are left with washing machine maybe,is it hot and mains cold supply
any thing else downstairs that is connected to hot and cold

[pg1066]

The problem first occured when house was empty for several days. Now it occurs 2 or 3 times a month. Usually afternoons when house has been empty during day.

Cylinder expansion pipe is clear of water level.

I will need to check on how washing machine is connected tomorrow. How would the mains water flow back through the hot water from the washing machine? does the washing machine, if fed from hot and cold, have a mixing valve that would allow this to happen?

Thanks for the suggestions.

[Puddle]

so it looks like slow leak into hot from mains and over flows as hot or cold not used to empty tank at all

The washing machine has plastic inlet casing up to opening solenoid valves,this could have a hair line crack between both supplies
if hot and cold fill,isolate and disconnect hot supply hose from isolation valve and place in bucket,leave cold connected,see if bucket fills over period of time ,if so ,that is your problem

[pg1066]

Thanks
Will try that tomorrow.