Fault on Honeywell st9400c

[Callum Curwood]

Hello. Just been to look at a job for a friend. The programmer is a Honeywell st9400c and when it is put on auto or manual programme the programmer keeps cutting out and restarting it self and the boiler. The programmer is keeping all it's settings but sometimes clicks on and off a few times then stays on for a while then keeps clicking again. Any suggestions would be much appreciated, thanks

 

[Simon F]

:welcome:to the forum.
fit a new programmer??

 

[Ermintrude]

Check it's on the faceplate and no loose connections

 

[Callum Curwood]

A few things popped up when I wa looking. When switching between C/H and H/W they was no noise/ movement on the 3-port valve so I don't know if its the valve or the programmer. Just wondered if anyone's had the problem?

 

[armyash]

Had similar and turned out it was the programmer.

After changing the 3 port 😀

 

[ogg]

I have the same issue with st9400c programmer which powers off and back on after starting boiler. Programmer power is fine normally it only cuts out when the timer is trying to switch on HW.Valve starts to open then closes when the programmer goes off.

Will check connection but probably just buy new one.

 

[Callum Curwood]

I put a new programmer on and it all worked fine afterwards. All connections on the backplate and wiring centre were all tight.

 

[Bobbieb]

I have a ST9400C which worked OK but every few days the heating switches from "Auto" to "off" - usually in the night so no heat in the morning. The hot water works OK even when this happens. Replaced the programmer and same fault is happening again, even though I left it on the factory default program. Any ideas welcome.