Britony Combi 80... nearly solved

P

PaulScrivens

For a few months now my boiler has been playing up. Basically when drawing water or turning on CH the boiler will fire up, the flame will light then go out after about 8 seconds.

This was a temperamental problem. Leaving the boiler off for a day, or so, will give a few days of service. However, only if I disconnect the plug connected to the 2/3 gas stage switch (stops boiler going into full flame).

After having a plumber look at my boiler and replace 3 way valve, service the boiler and change the overflow thing, I decided to Phone Chaffoteaux and Maury myself.

Turns out the heating thermistor temp sensor is faulty. which was diagnosed by disconnected both plugs connected to the termistor and plugging the heating plug in to the HW thermistor. I have ordered a new one which should solve my first problem.

Second problem: When drawing hot water I reconnected the 1/3 gas stage plug (described above). When I do this the boiler starts to makes a loud hissing/whirring noise. Apparently this is caused by sludge in the heat exchanger which can be solved by flushing.

How do I go about this? I assume I can open up the boiler, disconnect the heat exchanger and somehow fill it with some chemical? Is this an easy job? do I need anything else? e.g. hose? What chemical should I use?

Many thanks in advance for any help

And I hope this is useful to people with similar problems.
 
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OK, thermistor replaced. In the excitment of, at last, having a working boiler I forgot to drain the system!!! Water everywhere!! quite lucky there are no electic points nearby!

I have also added Sentinal X400 into the system to remove the sludge. It's been in 2 days now and the noise is slowly disappearing.

Now I have 2 more questions:

I have noticed the water seeping out of the Air Seperator. The red cap is screwed on tightly however water still comes out and sometimes fills the trough it is screwed into. I guess this part needs replacing? Should the red cap be tightly screwed in?

Second question: I have noticed that when turning off the CH the flame goes out but the boiler does not completely shut off for about 3 mins. Is this as designed? I can't remember if it shut off when it was working properly about a year ago!!! :-S
 
The AAV plastic cap should not be tight but loose to allow air to escape. They frequently leak water but it may stop doing so as a result of chemical cleansing. You could take the top off and try cleaning it (drain boiler first!).

The pump will continue running after the burner extinguishes. This is to dissipate heat in the heat exchanger and is normal.
 

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