ST699 to ST9400c

[Debbo81]

Hi All,

Please help!! I have just replaced my old st699 with the st9400c. I followed the wiring swap to the letter including removing the bridge from old L-5 and 5-8. No problems at all with hot water but cannot get heating to fire at all despite programmer showing green light and wall stat showing red light as active. From what I can gather, I have an old Y plan system. I stupidly did not take a picture of old wiring but had labelled each wire and then removed labels upon refitting into new. There was no other wire connected to 8 on old programmer, just the bridge. It's also worth noting that when I turn heating on.. I can hear the port valve moving over. Any suggestions at all please and thanks

 

[Stuckinarut]

If the 3 port valve is moving over, then perhaps the issue is with that not making the microswitch, rather than the new st9400c. Any photos of wiring? Any voltage testing equipment?

 

[stem]

removing the bridge from old L-5 and 5-8.....There was no other wire connected to 8 on old programmer, just the bridge.

All of that sounds fine, Also, the wire that was in ST699 terminal 3 (CH On), should now be in the ST9400C terminal 4 (CH On). Is that how it is? The reason I ask is because.......

It's also worth noting that when I turn heating on.. I can hear the port valve moving over. Any suggestions at all please and thanks

You don't normally hear the valve moving to the heating position. Normally it's only audible (whirring noise) when it moves away from the heating position.