Combi boiler central heating problem

27 Mar 2012
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United Kingdom

I have a Worcester cdi rsf combi boiler, it is I'd say 8-10 years old. Today the heating didn't come on this morning. It has a little clock on the front, that has a dial with arrow pointing and a switch on it that goes from 0 to I. It is on I for clock on.

I am suspecting the clock to be faulty. But when fault-finding it seems a bit confusing. I have removed the mechanical clock from the boiler, removing the 4 wire links from it (with it turned off of course).

The is a permanent live and neutral connection to the M connections. And a switch connection between the other 2 terminals, 5 and 3.

When testing for continuity the meter always buzzes and shows 0 resistance. Which I am confused about, as surely that means it's OK? It seems to buzz and show 0 resistance on all settings :oops:

How does the clock work? I'd have thought it made continuity at the set times ie between 6 and 8 when the black clogs were set?
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Presumably you are checking continuity between 3 and 5.

Check continuity with the switch set to 0; it should be open circuit (infinite resistance).

0 normally means boiler permanently OFF, and 1 that boiler is permanently ON. There should be an intermediate position (sometimes called Auto) which means that the boiler goes ON and OFF according to the times set on the clock.

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