biasi he combi not reponding to room thermostat

[davejenks]

last night i noticed the room was cool and went to turn the heating on via the room stat (horstmann) which had the flame symbol to say the stat was telling the boiler to work. the boiler had 1 light on to say all ok in standby mode. i disconnected the room stat from the boiler and refitted the wire link and turned it on it cut in and all seems ok. i went and exchanged the stat for a new one thinking it was broke from screwfix (same type) with new batteries. it seems to turn on and when it reaches the temp cuts out but doesnt want to cut back in when temp drops. ive also checked the wire from boiler to room and it ok for continuety. . thanks

 

[Rob]

How much did the temp drop on the stat?

 

[davejenks]

room temp norm 21 c stat said 18/19. it has a 1 degree cutin so at 20 it would power up. as i say it had the symbol to say it should be fired up

 

[Agile]

If your boiler is an early M96 with two PCBs then there a fairly rare fault on the PCB which can stop the heating coming on again after reaching the stat temperature.

But that is usually reset if a tap is turned on.

Does turning on a tap reset it???

Can you measure the voltage across the thermostat connections at the boiler to see if the signal from the stat reaches the boiler?


Tony

 

[davejenks]

thanks tony, it has seemed to have righted itself somehow.the signal from the stat to the boiler is this a constant voltage when it wants it to turn on. i have a electrical power tester which shows certain voltages from 12v to 240v and continuity.

 

[Agile]

The voltage between the two wires will be zero when the stat is calling for heat!

Tony