Thermostatic mixer tap problem

[romboot]

Hi, I'm hoping someone can help me, I fitted a thermostatic bath mixer taps (sirrus) replacing a standard bath mixer taps, the system works off gravity only and I do not have central heating.
All appeared well until this evening when water is coming out of the tank overflow. I have checked the ball cock and all is well there.
It appears it is filling up from the vent (return) pipe.
There is only the stopcock downstairs by the cold water tap and a shut of valve inthe supply pipe to the emmersion tank.
Anyone got any idea what has happened please?

 

[oilman]

is the cold feed to the bath mains cold water?

Turn off the main stop tap and leave the kitchen cold tap on and see if the bath tap still produces cold water. If the cold water has stopped then you require a non-return valve on the hot pipe to the mixer and better to fit one on both pipes

 

[romboot]

Thank you, I have just cecked and yes the bath cold water has stopped running.
I will get a couple of valves tomorrow.
In the meantime should I leave the mains tap turned off to stop it overflowing or isthere something else I can do?

 

[Puddle]

No you will have to keep turned off,you would be better running a cold feed to shower from tank,by just putting a non return valve and pressure reducer in,even if the shower works ok, you are breaking water regulations and carrying out bad plumbing practices

 

[romboot]

The plumbing has not been changed from the day the house was built. Am I breaking regulations because a shower should not be fitted this way?
When I pump the cold water from the tank do I still need non return valves?

 

[Puddle]

The plumbing has not been changed from the day the house was built. Am I breaking regulations because a shower should not be fitted this way?
When I pump the cold water from the tank do I still need non return valves?

Yes it is fitting the shower mixer on your system that has caused the issue,hot tank feed,cold mains
If you run cold feed from tank and fit pump,making installation correct, non return valves will be fitted in pump but for differant reasons

 

[oilman]

if the cold water is changed to be taken from the cold water cistern as the hot water is already, then the pressures of hot and cold water into the new mixer are similar and isolated from the cold mains by the air gap on the part 2 valve filling the cistern so you would not require non return valves in this case as you could not contaminate the drinking purity of the main

 

[romboot]

Thanks for all your advice people. This is getting above my level of expertise so I will contact a plumber in the morning.
This all sounds expensive lol but I'd rather have it done right.
Amazing what you learn.
Why didn't it do it with standard mixer taps?