Honeywell ST699 randomly turning off

29 Sep 2022
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United Kingdom
Hi all,

I wonder if anyone could help me.

I've moved in to a new house about 2 month ago and the house has a Honeywell ST699 as the timer. A few days after moving in we saw the timer playing up, turning off randomly and not coming back on. Had a local plumber come in to do a service on the boiler and they said to replace the timer with a new ST699, which we did. Bought a brand new unit off ebay. This seemed to solve the problems we were having but two times now the timer has randomly turned off and the only to get it to turn back on was to press the re-set button. Has anyone else had the same problem?

Best Regards,

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Have you checked the wiring? Can you be sure the eBay one was correct? You could try replacing it with a completely different timer?
ST699 has a nicad cell in it. It is often dead so interruption of mains power will result in display going to 00:00

Other times, power supply that runs the electronics will have failed that overloads when relays (there are two inside one each for CH and HW) within operate. Overload means it shuts down and then starts again.
  • Thanks
Reactions: CBW
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How new is your 'new' unit from Ebay? The date code will be on the back plate. If it is old stock, the internal battery may have failed through age so will be susceptible to power variations.

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