Honeywell St699 problems I can't find any examples of this.

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forgive the basic errors I'm not an expert on any of this. We have a hot water tank and gas central heating it is controlled by a dial thermostat and a Honeywell st699. The one day two cycle one...

If the system calls for hot water OR central heating then there is no issue and it works fine, however if it calls for both via timer and hen thermostat for heat the system appears to trip. The st699 goes blank and the digital display disappears as do the orange lights. To reset the system all I have to do is turn the power on and off again and then the system works fine again until the call for both occurs again and the process starts again! The time is fine after the local trip so the battery must be ok but I can't figure what is gong on as I don't have to reset a circuit breaker or change a fuse, it's literally a turn it off and on again fix that I'm having to do twice a day!

All ideas welcome
 
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Sounds like the ST699 is somehow losing it's mains power supply, maybe due to some non standard wiring?? Has the system been modified recently and can you safely trace where it gets it's Live and Neutral feeds from?
 
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Thanks for the suggestions

Hasn't been changed since we moved in two years ago. It did this once a while back. The thing that. Can't get my head round is that it's not tripping anything the circuit is still complete to get it back working it's a fused switch next to the boiler I click off and back on! Haven't checked the wiring yet, going to call some support n for that...
 

DP

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Looks like power supply has gone to pot hence full load ( both channels) causes it to shut down. Time to change. Programmers have evolved a fair bit since ST 699 was born
 
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I have exactly the same problem. I am looking to replace the st699 with the st799 but I cannot fathom how to lift the panel out. I can't see any screws other holes in order to release and lift the main body. I understand I can ipad in a replacement without any rewiring.
Any suggestions much appreciated.
 
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I have exactly the same problem. I am looking to replace the st699 with the st799 but I cannot fathom how to lift the panel out. I can't see any screws other holes in order to release and lift the main body. I understand I can ipad in a replacement without any rewiring.
Any suggestions much appreciated.

There are 2 little slits on top, get a flat head screw driver and push into them while pulling the panel from the top gently it will click open and come off.
 
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Many thanks. I saw those and tried them but obviously not hard enough, I'll try again.
 
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I think you will find you need to push in a tab on the bottom right(?) corner and the unit lifts up off the top clips.
 

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