i have an unvented water cylinder and hot water is coming from the overflow how do i find and fix the problem

g*, January 2011

There is NO "overflow" pipe on an unvented cylinder!!! There is a D1 pipe which carries water from the cylinder to the tundish and there is a D2 pipe which discharges water from the tundish to an appropriate dispersal point!
Problem could be a faulty Temperature relief valve or a faulty Expansion valve or a faulty Expansion vessel

Dont mess about with this, get a qualified plumber who holds a G3 qualification to have a look at it!

Ram It, March 2011

1. is water venting from overflow hot or cold
2. does it only vent when tank is heating
3. if hot, pressure/temperature relief valve is probably faulty
4.if cold and there isn't an expansion vessel the tank air gap will require regenerating

toptrish, January 2011

the overflow vents when water temperature gets too high and then resets automatically so either the cylinder stat needs turning down or may need replacing or dirt is stopping the overflow valve from resetting properly though this would cause the overflow to run all the time

brian, January 2011