poterton suprema ch will not shut down

[neilski]

hi,
hope someone can help when the ch should shut down after being set on timer it carries on even if i turn thermostat down(room) it makes no difference.i turned off ch on timer before i went to bed and room hermostat down to min at 11.00pm woke up at 4.00am boiling rads hot on the timer hw is on as it is all the time(not sure if thats a good idea or not)
but i turned it off hw and that seems to have done the trick.but this is surely not normal do i make sense i'm sure any help would greatly appreciated
thanks

 

[Bahco]

Timer could be faulty or wiring needs checking.

 

[neilski]

you suggest maybe a new timer but room stat is on min timer selector for ch in off position hw is on the on pos and it the rads are boiling and the only way i can shut ch off is too turn hw into off pos and shut it all down sorry if i am repeating myself ,bit if the timer is faulty would that affect the room stat
thanks for your reply

 

[Bahco]

Do you have a y plan system. If so, I'm thinking it could be a 3 port valve not moving into hot water only mode when thermostat is satisfied.

 

[croydoncorgi]

If the boiler is continuing to fire either something is telling it do so (ie. a 3-port or zone valve, or theirs a dangerous fault on the boiler itself.

Thermostats (on cylinder and room stat) should ALWAYS be wired between programmer / timer and motorised valve(s), so if the rads are getting hot presumably the roomstat should turn off. If the boiler is STILL firing, then is the hot water at the set temperature? If not, the ZV / 3-port is jammed in CH position. If the water is not fully hot when the fault has occurred AND you have a 3-port valve (Y-plan), check whether the boiler shuts if you turn the cylinder stat DOWN. If so, it's the 3-port that's the problem. If the boiler still runs with both stats turned down, it has to be a wiring problem or a boiler fault. But then, Suprimas most often have completely the opposite problem!!!