Honeywell st699 turning off on its own

[Djjohn69]

Hi all. I have a problem with an st699 programmer. It's on a c plan system with gravity water and pumped heating. The problem is the same for heating and hot water setting. Programmer light turns off and on a few times turning boiler off before staying off until electrical supply is turned off and back on. Occasionally boiler does stop on after this process but is getting less frequent. System has had a new pump and 2 port valve in recent years but boiler and programmer are around 20 years old. Any help would be appreciated

 

[CBW]

I’m led to believe they have a battery in them, if it’s not this, then might just be time for a new one.

 

[ianmcd]

I’m led to believe they have a battery in them, if it’s not this, then might just be time for a new one.

But its only 20 years old surely there is a valve or something I can replace

 

[mcprinter]

My ST699 is only about 15 Years old.
Some used ones on Ebay or a new one for a bargain £400
Very easy to swap like for like. Did mine 15 Years ago.

Probably best replacing with something more modern.
Unlikely to find something that will fit the backplate. Will need to know what you are doing or call someone in.

 

[CBW]

But its only 20 years old surely there is a valve or something I can replace

Isn’t it always the pcb 1st? Then guess a load of parts?

 

[DP]

The battery will be l9ng dead. Indication of which is power outage leads to display reverting to 12:00

Main circuit will be problematic on the power supply section. When the programmer chip operates relay, power goes down and display reverts to 12:00