C/H overflow to vent pipe.

[rogerc]

I have a Potterton gas boiler feeding a gravity system with Grundfos circulator.

When the circulator switches on there is an immediate rush of water from the vent pipe to the header tank. After about 30 seconds when about a litre has been discharged the flow stops and the c/h behaves as normal.

I have introduced restorer to the primary circuit to clear sludge etc. but still have the overflow problem. The pipework was revised about 15 years ago when the new boiler was fitted - the family tells me that this problem has only occured in the last couple of months though. Any ideas?

 

[oilman]

It could be (but it might not), the feed pipe from the header tank is getting obstructed. You will have to drain some water from the system and see if the tank level goes down and recovers. If you have put cleaner in the system it should be flushed out, as the cleaner merely lowers surface tension, it doesn't magic the debris away.