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Michael, Customer Service
Category: Appliance
Satisfied Customers: 9568
Experience:  I have been an appliance repair tech for over 30 years and will help you solve your problems.
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Hi, I have a Worcester Heatslave 20/25 oil-fired combi

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I have a Worcester Heatslave 20/25 oil-fired combi boiler. The hot water part of it works fine, but when the heating switches on (either by timer or manual switching on) the boiler doesn't fire.
I've found that a good smack on the side at the top front left corner makes it work instantly, but that isn't much good now I wanting coming on while we're out/in bed.
Happy to pay for any answer, even if it's just "get an engineer out now" as this will get it fixed quickly.
Thanks in advance!
Hi, this is a bad controller or simply a loose wire on the unit.
My suggestion to you would be to re tighten the connections to the control at the boiler. If that works GREAT! But if it doesn't, then you have a failing relay on the board more than likely.
I will stick with you until this is fixed, please don't forget to rate my service to you before you close this page. I will be available to you at no additional cost , you can then get in touch with me anytime by simply replying to this message.
Thank you and have a great day!
Tech Michael
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Customer: replied 3 years ago.

Hi Michael,

Thanks for the reply. Please can you describe where in the boiler I should be looking for/tightening connections. I haven't been inside it yet, so would appreciate a pointer where to start.


Hi Dave, you want to look at the control box, its basically a relay device. Its where you would likely see a light(LED).
Its more than likely going to need to be replaced, but it could be a loose wire as that would cause exactly what you describe.