Hello, Just joined. I value any ones advice here please.

I have a Baxi back boiler in the living room inside the fireplace. The primary circuit (from the heat exchangers to the cylinder) seems to bubble like mad and occasionally clatters waking me up at night and irritating me during the day. This I want to cure because there must be air in the system and I do not know how to 'bleed' it.

The HW must be on to work the CH. Both produce piping hot water happily but the problem noise (and I guess poorer energy efficiency) does not go away.

I can not seem to find a bleed valve anywhere on the primary circuit to or on the pipes leading to or from the cylinder. The header tank was cleaned and the CH system was thoroughly drained and flushed and topped up with Fernox during the summer. The radiators were (eventually) bled fully by late October, I have not needed to do these since and the rads appear fine now. Recently I have noticed that the header tank now has a black scum on the surface of the water.

Much appreciated.

corkgasket, December 2010

yeb sounds like the state, or i have had a gas valve not fully shutting off so the boiler keeps getting hot, you need a gas safe eng to check it out

erj, December 2010

The problem will be either:
A faulty thermostat:
Scale in the heat exchanger, often happens in unprotected gravity systems (I suspect you added inhibitor as an afterthought)?

1: New thermostat
2: Add a descaler (brand name Sentinel x200 {but there are other makes} into the primary system)

Carefree, December 2010