chimney sweep mode

5 May 2008
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United Kingdom
hi. if a boiler wont fire up for central heating demand but fires up chimney sweep mode doesnt that quickly tell you that its the external controls ie roomstat, timer thats the cause since the boiler firede up for chimney mode it must be ok. talking about worcester greenstars, valliants. thanks
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Your correct. On a Vaillant the plus and minus simultaneously enter service/chimney sweep mode. This is a quick test to prove the majority of boiler works fine (fan, gas valve, ignition, pump etc etc)
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so if its working on service mode but not on central mode as per normal then this confirms that roomstat/timer are the cause??
It might indicate that but not necessarily so!

It could be a boiler PCB fault or a sensor out of calibrationetc.

Assuming it is a Vaillant terminals 3 & 4 need to be linked out on the pcb. If the boiler then works fine it is an external control problem.

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