Chafeteau system boiler lockout

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23 Apr 2009
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Location
Somerset
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United Kingdom
We have a chafeteau and Maury system boiler (gas). It is about 8 years old and has been regularly serviced. A couple of weeks ago it locked out - the red lockout light was illuminated.

The reset button does not bring it back to life. If it is turned off and then back on it will ignite and the radiators start to heat up for a short while and then locks out again. All the radiators have been bled and the system has enough water as indicated by the bar pressure guage. Most of the time the system will lockout after only a few minutes of running.

A plumber came (one that we have used before and is good) and spent an afternoon checking everything out - all the sensors etc. This was to no avail and so he phoned the manufacturers helpdesk and was advised that the most likely cause was the PCB (at least I think that was what he said!). Anyway he got a new PCB which he installed but it made no difference.

Another call to the manufacturer left him scratching his head in bewilderment. He then took off the metal cover that protects the actual gas burners. He was then able to restart the boiler which ran as normal. At least it seemed to run ok - the green temperature lights fluctuated between 3 and 4. He then replaced the cover and the boiler stayed on.

However after that when turning on and off the dreaded red light re-appeared straight away. This taking the cover off thing may of course be a red herring!

Anyway, the plumber is returning in a few days to have another look but if anyone can offer any advice PLEASE.
 
Air pressure switch changed and although it's early days it does seem to have sorted the lockout problem.

Engineer is still not happy because he says the boiler is firing up and shutting off too frequently. He thinks the fan also needs replacing as he says he has measured the output of the fan and it is below the minimum required by the boiler. Trouble is that this is going to be another £150 at least.

Can you advise if this is really necessary.
 
Have been running with new air prssure switch for 4 days. Seems ok when central heating is on, although it is still doing the short cycling thing. However when the boiler is on for hot water only it is locking out after having been on for about 20 minutes.

Don'y know if this helps diagnose the real issue. Still reluctant to go for new fan as suggested by plumber.
 
venturi in the fan should be looked it...if it has one? not sure of this model, but it might just need cleaning. Other than that, possible a blocked filter of some sort? again I don't know if it has one! maybe someone who's worked on one can confirm?
 

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