Venting problems

[Neil]

Hi all, I recently had a shower fitted, not electric, the mixing bar type, the plumber who fitted it only used a single pump, which was not suitable because the cold water to the shower is mains fed and the pressure of the cold water was stopping the hot water getting into the mixing bar, to solve this problem instead of fitting a twin pump, he fitted a water pressure reduction valve to the cold water feed to the shower. The shower now works, but I noticed the warning pipe was constanly dribbling water out. I checked the ball valve in the cold water tank which seems to be working fine. But when the warning pipe starts to vent water, the water level in the tank is above the overflow, but the ball valve is shut. I can only presume the excess water is coming from the vent pipe from the hotwater tank. Has anyone got any idea why this is happening?

[TheScullster]

"Neil" wrote

If I understand correctly, since the shower was fitted, water has been overflowing from the main water storage tank in the loft. You have tested the ball valve and are confident that this is not passing at all.

If these assumptions are correct then I would suspect that the shower is passing internally such that water on the cold side under mains pressure is backfilling the storage tank via the hot supply pipe work.

Did the plumber fit isolation valves on hot and cold supplies so you could isolate the shower? How long does it take for the overflow situation to develop?

To check if it is the shower just:

Leave the system as it is and monitor the level in the storage tank (do not draw off hot water, or cold water supplied from the storage tank during monitoring period of course). Decide how long it takes for the water level to rise a given distance. Turn off hot and cold supplies to shower. Draw off water from the storage tank to float valve set level. Monitor the storage tank level over the relevant time period used above.

If there is no change in water level with the shower valved off, then it is likely that the shower is at fault.

The only other explanation for this that I am aware of is a leaking coil in the HW cylinder allowing central heating system primary circuit water into the domestic water. This would normally be accompanied by dirty hot water.

HTH

Phil

[Christian McArdle]

Can you confirm where the single impellor pump is?

Is it on the hot water supply line, or on the combined output from the mixer?

The backfilling on the tank is because he forgot to install check valves on the shower valve supply lines.

Christian.

[Neil]

Thanks for replying christian, the tank is back filling, the cold water pipe supplying the Hot water tank felt warm and when I shone a torch into the cold water tank i could see water flowing back in, if I installed a check valve on this pipe would that stop the problem.

[Christian McArdle]

Yes, but ensure it is fitted just before the shower valve. DO NOT put it on the feed to the hot water cylinder. That would be dangerous and wouldn't even work. Ensure one is on the cold mains supply to the valve, too.

Christian.