Leak from boiler/CH losing pressure

28 Dec 2011
Reaction score
United Kingdom

I moved house recently and one issue that I noticed after a week or so was lots of trapped air in the CH. Two or three upstairs radiators had about 1/2 to 1/3 of the top feel cold. The system also had too little pressure to force this air out when bleeding the radiators (the boiler read around 0.7 or 0.8 bar).

I topped up the CH using the mains inlet at the boiler, and bled off the air. All seemed fine and I assumed that was that. However, I've noticed that the boiler has a leak at the diverter valve, that the pressure drops again and air slowly gets back in.

I plan to get someone to look at the boiler and hopefully replace the leaky valve (hoping this isn't a more terminal problem for the boiler) and hopefully sort this. I'm just a bit puzzled by the amount of water leaking and the corresponding drop in pressure, though. After topping up the boiler to between 1-1.5 bar, it will leak about 2 tablespoons worth of water from the valve over the course of about 1 day, and the pressure will drop to 0.8 bar or so. This feels like a big drop in pressure for such a small leak, so I'm worried there's another leak elsewhere.

Does this seem to make sense, or does this suggest there might be another problem somewhere else? I've had a good look around the CH pipes for other leaks, but found no evidence of any so far either internally or in the pipes running under the house.

Just wanting to know if I should be looking for another problem before I call someone out. Thanks!

p.s. boiler is a Worcester Bosch 35 CDi II installed in 2009
Sponsored Links