Water overflowing when pump kicks in.

[Talus]

My central heating system (open vented) is fuelled by a wood-burning stove. After it has been lit for a while and the pump kicks in, water begins to trickle from the overflow pipe coming from the feed and expansion tank. After a while this reduces to a steady drip. Hoping someone can tell me what the problem may be.

 

[GasAid]

Pipes incorrectly configured and a blockage developing somewhere near the feed and vent - Try turning the pump speed down as a temp solution.

 

[holty]

maybe the ballcock is slighty letting water through, then on expansion of the water when getting hot ,the water level will rise above the overflow. check ballcock, to see if theres a slight drip coming from it. if so replace the washer.

 

[Softus]

maybe the ballcock is slighty letting water through, then on expansion of the water when getting hot ,the water level will rise above the overflow. check ballcock, to see if theres a slight drip coming from it. if so replace the washer.

Hogwash. The system is pumping over. As GasAid said, it's probably becoming blocked.

 

[holty]

so softus what iv sugested is unheard of.

 

[Softus]

I apologise and retract my previous post.

What happened was that I misread what the OP had written.

There are two possibilities:

1. As per holty's suggestion, leaking float valve;
2. Cylinder coil split or corroded.

 

[holty]

thanks for the apology softus, we'v all miss read things before, but forgot about to mention the pinholed coil well stated.

 

[Talus]

Thanks for the replies. It should n't be the ballcock as I replaced the whole thing. I have also turned down the pump to setting 4 then 3 (Max 5) and it is still overflowing. Looks like it must be the coil.

 

[nickso]

Thanks for the replies. It should n't be the ballcock as I replaced the whole thing. I have also turned down the pump to setting 4 then 3 (Max 5) and it is still overflowing. Looks like it must be the coil.

you say it only happens when the system is being heated?

as per holty, what height is the water in the f+e at when its cold?

if it was the cylinder coil i wouldnt have thought hot or cold would make a difference. usually drips all the time if the coil is gone.

 

[Talus]

I was in hospital for most of the summer and my partner informed me on my return that there was a very slow drip from the overflow - which is why I had the ballcock replaced. At this point the logburner was not being used - but the immersion was on solely for hot water. Unfortunately due to my injuries I was not (and still cannot) access the loft.

 

[nickso]

if its dripping all the time then it could be the coil or certain types of mixer taps/showers if faulty can cause the mains to back fill the cylinder. you can usually hear the tap/shower doing this if its a fast enough leak.