Expansion tank problems

[andy gee]

I'm hoping that someone can help me. (I'm not a plumber but have a little idea of things.)

My heating/hot water system comprises of a cold water header tank in the loft, a hot water cylinder in the airing cupboard with a pump and zone valves for HW & CH and an expansion tank in the loft.

The problem I have is that recently water has started to continuously feed from the vent pipe into the expansion tank. The vent pipe feeds from the pipe that comes from the boiler and goes to the pump. There is another pipe that feeds from the bottom of the expansion tank straight back to the boiler/pump pipe, only inches away from the vent pipe, so the water level in the expansion tank does not rise at all.

The hot water is not overheating, which rules out a faulty tank thermostat, ther water circulates into the expansion tank even when cold, which indicates that there is no problem with the boiler thermostat and all the radiators work perfectly, which indicates that there is no blockage in the system.

I am sure that this is something simple which I can't see for looking!

Does anyone have any ideas please?

 

[Briteheat]

Sounds like you have a partial blockage in the cold feed connection. Cut out the section of the primary flow containing the cold feed and primary vent and clean it out. I always reinstate this section of pipework using compression fittings and a sealing compound (e.g. Fernox LSX) to facilitate removal if the problem occurs again. Hope this helps.