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Andrew Smith
Andrew Smith, Engineer
Category: UK Plumbing
Satisfied Customers: 3629
Experience:  Domestic Gas, Commercial Gas, LPG, Unvented Hot Water, Part P Electrical, Commercial Catering
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I have 2 thermostats feeding into a Honeywell ST9400C

Customer Question

Hi, I have 2 thermostats feeding into a Honeywell ST9400C programmer. One thermostat is for downstairs the other for upstairs. The one for upstairs is working fine however when the temperature called for the boiler to come on and kick the radiators into action nothing happens. The thermostat clicks and the flame symbol comes on but no reaction from the boiler. I have swapped the 2 thermostats over and this hasn't helped. The boiler works for hot water and radiators upstairs but not downstairs. The programmer is not one of the 'dodgy' batches I have read about. Is it possible that the programmer just needs replacing?
JA: How long has this been going on? And how severe is the problem?
Customer: It started before summer but we put it off because we have solar panels and didn't need the heating.
JA: Do you plan on doing the work yourself?
Customer: If it's simple yes! If it involves plumbing and anything more than replacing the programmer then no
JA: Anything else we should know to help you best?
Customer: Don't think so
Submitted: 10 months ago.
Category: UK Plumbing
Expert:  Andrew Smith replied 10 months ago.

You will find it will be a problem with the motorised valve, it should open when the heating is requested from the programmer

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