Ariston 23 combi.

[jncalderc]

Out today at a call out ariston combi 23 mffi. It feeds a 3 storey underfloor system split into zones. Basement ground first. Turned it to summer so no dhw problem. Doesn't matter how low any of the stats are the boiler still runs at full pelt. Tried turning temp down on boiler to 1 but still runs on and house is like a sauna. Ended up switching off and leaving but could it be the PCB on its road out. Will need to disconnect stats on the PCB but this would only show stats were the problem not prove it was the PCB would it?

 

[Billy Bob Bob]

if the ch thermistor is shot or got wet this will cause it,look for about 11-12k cold above this you need a new thermistor if it checks out ok pcb has failed

 

[jncalderc]

hmmm, along the lines of what I thought, I found another time clock on the job in a box it has obv been replaced by someone who I reckon thought it may have been to blame and replaced it, possibly previous client will go back tomorrow and see what comes from a more detailed look.

 

[jncalderc]

Changed the thermister and the boiler fired fine but wouldnt switch off or go off under timed. Checked out the old clock that was on the site and found there to be no problem with that or the one which was fitted just connected wrong from the board. The wiring from the PCB is red to 1 black linked to 2+3 4 Empty 5 grey. NO doubt u know this but it will remain on here as a memory jog for myself if ever i hit the same prob.

 

[jncalderc]

incidentally reason the boiler wasnt taking command from the stats is that the stats had been terminated in a terminal block inside the casing and the stat on the boiler linked out.
Didnt want the hassle of going through the issues so left as is.

 

[Billy Bob Bob]

thats unusual somebody messed with that big style i would do the same walk away