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Everything was working last night but no hot water this morning. Things I have checked:

  • gas supply to the house is fine
  • electricity is going to the boiler
  • fuses are good
  • sounds like the water pump is working
  • thermostats click correctly

But there is no spark, and not even the usual click for the igniter.

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Do you hear/smell gas flowing? Is there a way to manually open the gas valve on your heater? – Tester101 Sep 27 '12 at 17:35
Does this heater use a pilot light and is it lit? – The Evil Greebo Sep 27 '12 at 17:44
Could be a bad ignitor, bad ignition control module, bad ignitor wire(s), or even a bad thermostat. Is there a blower motor on your unit? – Tester101 Sep 27 '12 at 18:21
Gas is one of those things that are risky for a DIYer unless you really know your plumbing. If you cannot fix it after checking the pilot and ignitor dsicussed above, I urge you to call a plumber. A minor flashback with a bad pilot light just singed me but burned the desire to fix gas myself right out of me. – bib Sep 27 '12 at 20:28
+1 for a bad ignitor. – mikes Sep 27 '12 at 21:24
up vote 4 down vote accepted

The good thing is - the nice man from Scottish Gas fixed it for me. Diagnosis took about 20 seconds - he knew before he had the cover off.

He couldn't hear the impeller fan running. Turns out the motor was over 16 years old and had just died. Because it wasn't drawing any air, the pressure sensor kept the ignition circuit off and the gas valve closed as a safety measure.

One swift replacement later (he had one in the van) and it worked straight away.

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