Honeywell ST9400c Water but no heating

Kevindurant

We could not get Honeywell ST9400c thermostat on when we moved in , turns out the on switch was in a different cupboard. We got a plumber out , he tested heating and it worked in minutes.  Today we cannot get heating to come on despite the thermostat being on continuous. Lights all work but when I tried to “add one hour” etc it did say invalid but allows me add one  hour for water. Any ideas ?? There can’t be anything wrong if plumber checked it just a few weeks ago. We must be doing something daft. Thanks in advance 

tacpot12

The only mention in the manual for the ST9400c of an "invalid" message is a "not valid" message that occurs if the Thermostat has been configured as a Mini-programmer. This configuration basically means that the heating and water both come on together, so if you add 1 hour for water, you are also adding 1 hour for heat. 
Have a look at pages 15 and 16 in the downloadable version of the manual here: 
Honeywell ST9400C 7day Programmer (heatingcontrolsonline.co.uk)
It suggests you need your plumber to say whether this is correct for your system. It would be worth finding out from your plumber whether you have a fully pumped system or a gravity system, and whether it is wired as per any of the Honeywell Plans, e.g. S-Plan, Y-Plan, C-Plan, W-Plan.  

Jack_Cork

Excellent answer from tacpot12. You need to ascertain if you can indeed run CH without HW, I know on older gravity feed systems this isnt possible, both have to run so therefore you cant have an extra hour CH on its own.
Correct me if I am wrong but if you have a pump and diversion T valve you should be able to control both separately? 

I just fitted the exact same controller a few weeks ago, and indeed if you cant control both separately you need to change the settings to 'mini-controller'. My system is fully pumped Y plan so can run CH/HW separately

Kevindurant

tacpot12 said:

The only mention in the manual for the ST9400c of an "invalid" message is a "not valid" message that occurs if the Thermostat has been configured as a Mini-programmer. This configuration basically means that the heating and water both come on together, so if you add 1 hour for water, you are also adding 1 hour for heat. 
Have a look at pages 15 and 16 in the downloadable version of the manual here: 
Honeywell ST9400C 7day Programmer (heatingcontrolsonline.co.uk)
It suggests you need your plumber to say whether this is correct for your system. It would be worth finding out from your plumber whether you have a fully pumped system or a gravity system, and whether it is wired as per any of the Honeywell Plans, e.g. S-Plan, Y-Plan, C-Plan, W-Plan.  

Sorry I should mention initially the water was on continuous and I tried to just put heating on THEN did the hour thing when nothing was happening . So even if both only come on together, the heating was still not coming on. I’ll check the other points. Thank you so much for your time answering. It’s very much appreciated. 

Kevindurant

Jack_Cork said:

Excellent answer from tacpot12. You need to ascertain if you can indeed run CH without HW, I know on older gravity feed systems this isnt possible, both have to run so therefore you cant have an extra hour CH on its own.
Correct me if I am wrong but if you have a pump and diversion T valve you should be able to control both separately? 

I just fitted the exact same controller a few weeks ago, and indeed if you cant control both separately you need to change the settings to 'mini-controller'. My system is fully pumped Y plan so can run CH/HW separately

Sorry I should mention initially the water was on continuous and I tried to just put heating on THEN did the hour thing when nothing was happening . So even if both only come on together, the heating was still not coming on. I’ll check the other points. Thank you so much for your time answering. It’s very much appreciated. I’ll try your advice on what type I have next 👍🏼

southcoastrgi

Room stat ?