help with honeywell st9400 heating controller

[killbillr1]

hi any help would be appreciated, woke up this morning and there was no power to my honeywell control unit totally blank. so i removed it from the back plate and got my multi meter (i’m no electrician) and put on the live and no reading, does it only go live when the boiler is on?

 

[CBW]

Which live did you test? Main live or switched? Where did you place the probes between which terminals?Have you checked the fuse for continuity/resistance? Have you checked the fused connection unit?

 

[killbillr1]

hi i put the red probe in the red wire and tried the black on all of them. i’m not sure on the rcd board where the heating system is, there’s one labelled immersion heater so it might be on that, if it is it’s fine as the immersion heater light is on next to the tank

 

[CBW]

hi i put the red probe in the red wire and tried the black on all of them. i’m not sure on the rcd board where the heating system is, there’s one labelled immersion heater so it might be on that, if it is it’s fine as the immersion heater light is on next to the tankView attachment 337773

Assuming you tested with the power on and checking Volts ac on the multimeter, you should have approx 230vac between L (red) and N (Black). I’m not talking about the rcd/mcb, nor the immersion - you should have a switch often in the vicinity of the programmer (Honeywell) but could be in the kitchen depends on your layout.

 

[killbillr1]

yes i tested with the power on but only a real basic meter, i thought it may have been faulty so tested it on a light switch and gave off a good reading so it works ok
there’s only one switch in the cupboard and that’s for the immersion heater on the tank
5 minutes ago the boiler came on, don’t know why or how as there’s only the backing plate on the wall and no controller attached. so i put the meter back on the red terminal and i now get a positive reading. can i now assume i need a new controller?

 

[CBW]

No I wouldn’t assume that just yet, as the boiler shouldn’t fire as there’s no demand. Odd how you’re now gettinga reading though, could be a loose connection somewhere. Could probably do with finding that switch - I highly doubt there’s isn’t one.

 

[killbillr1]

i thought the same about the boiler coming on. my other half said there was no light on on the boiler earlier on, then she heard it fire up momentarily then went off and is now displaying’0’.
there’s a big junction box below the back plate, every wire in all the terminal blocks are in there and tight, the only other switch is the one next to the boiler that powers that

 

[CBW]

the only other switch is the one next to the boiler that powers that

It could come from that tbh.

 

[killbillr1]

the plot thickens. so i turned off the power to the whole house, put the controller back on the back plate, fired up the power and the controller now fully works. so my only thought now is the boiler must have lost power at some point this morning ( my other half swears she didn’t accidentally turn the boiler switch off at the side of the microwave)
thank you for your suggestions CBW

 

[CBW]

No problem, glad you’re sorted.