Boiler not firing sometimes for DHW when cold!

5 Oct 2004
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United Kingdom
Hi all

I've a Ravenheat HE85T combi which recently has had a new (dry type) CH sensor and new diverter valve and microswitch.

I noticed a fault of intermittently boiler not firing for DHW when cold.

I replaced the microswitch with a new one but the fault came back again. Its very intermittent and generally comes when the boiler is ice cold...

Also of late, the boiler is sometimes taking a long time to fire off when the hot water tap is opened.. This is again intermittent and sometimes the boiler fires off when the hot water tap is closed e.g. the boiler does not fire when hot water is opened to wash hands and after the tap is closed, the boiler fires off for a few seconds, then switches off..

The CH is working fine and the DHW works fine as well when the CH is ON!

Any ideas where to look?

Thanks in advance...
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did you look to see if the pin frim the diaphram was sticking and not making cintact with the microswich
i tend to check the diaphram when i replace the m/swich ?
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gasandoilman, the pin from diverter is always coming out and as far as I can see, it is making contact with the microswitch..

It surely is as boiler is firing OK 90% of the times...

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