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JamesI
JamesI, Handyman
Category: Appliance
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Experience:  I have repaired and maintained numerous items over the years, from fridges to freezers, radios to TV's.
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We have a Honeywell ST772 sundial system, it has developed a

Resolved Question:

Hi there,
We have a Honeywell ST772 sundial system, it has developed a curious issue
When flipping the switch over to continuous the controller turns itself off after the boiler fires for 1 or 2 seconds , and will only come back on after pressing the reset button
Any suggestions?
Thanks
Submitted: 3 months ago.
Category: Appliance
Expert:  JamesI replied 3 months ago.

Good morning my name is ***** ***** I will assist with your query today.

Please give me a few minutes to look up your specific model

Customer: replied 3 months ago.
Cheers James
Expert:  JamesI replied 3 months ago.

So the controller display just goes blank when the boiler starts?

Customer: replied 3 months ago.
Correct, as soon as you switch to continuous the whole controller goes blank, never happened in the 10 years we have been her
Customer: replied 3 months ago.
It does work in timer mode after resetting , we are getting hot water in the morning?
Expert:  JamesI replied 3 months ago.

This sounds like a short on the circuit board, the switch is most likely faulty.

Are you able to induce it by pushing the switch half way over?

Expert:  JamesI replied 3 months ago.

Can you also try the same with moving the HW to continuous?

Customer: replied 3 months ago.
Would appear it's the heating switch causing the issue ,h/w seems to be ok , as soon as the heating switch clicks to continuous the unit goes blank
Customer: replied 3 months ago.
Yep just tried it again , heating switch seems ok on , once , twice or off but it doesn't like continuous....
Expert:  JamesI replied 3 months ago.

Ok that proves the fault, its nothing to do with the relay or boiler as the fault would occur each time the boiler started (on auto or continuous).

The cheapest option is to replace the timer, the Honeywell model which replaces your unit is the ST9400C, which costs around £70.

You could try and replace the switch but unless you have an electrical engineer background and handy with a soldering iron its beyond most peoples DIY skills.

Customer: replied 3 months ago.
Ok thanks James
Expert:  JamesI replied 3 months ago.

Since the fault only occurs on continuous, I might be inclined to leave it until it completely fails.

Customer: replied 3 months ago.
might be a good idea, it's not that cold yet..... Is there anyway I could get the heating on for longer without the continuous working?
Expert:  JamesI replied 3 months ago.

Give me a minute while I find the manual again.

Expert:  JamesI replied 3 months ago.

You can set the switch to "Once" - The heating will turn ON at the first ON time set and stay on until the last OFF time set each day.

Expert:  JamesI replied 3 months ago.

If you just want to override it, you can press the "change" button to the right of the switch, which will turn the CH on and stay on until either the timer tells it to switch off or you press the button again to manually turn it off.

Customer: replied 3 months ago.
That's interesting, just changed the times for the heating on and off to see if It would accept it, unit went blank again, looks like we have no heating unless I get it changed now...I think I need a new unit
Expert:  JamesI replied 3 months ago.

Its not a big job changing it, just make sure you switch off the power to the boiler (as that is what serves the timer.

I know Screwfix are selling this unit for about £80 if you want to pick it up today.

Customer: replied 3 months ago.
Thanks again James , it is the heating switch so I will probably go to screwing today
Customer: replied 3 months ago.
Damn spell checker, screwfix I meant to say!Apologies
Expert:  JamesI replied 3 months ago.

I wont blame you when you look at their prices!

Appreciate if you can rate the service received today.

Customer: replied 3 months ago.
Will do, I think Amazon have them for about £65 so I might just wait and tell the kids to put jumpers on!
Expert:  JamesI replied 3 months ago.

A quick google showed you can pick it up for £61.50 from here, including delivery or on ebay here for £58.99

JamesI, Handyman
Category: Appliance
Satisfied Customers: 806
Experience: I have repaired and maintained numerous items over the years, from fridges to freezers, radios to TV's.
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