boiler will not shut down automatically

[geoff holdcroft]

my central heating system will not switch off. After the set times on the programmer have been passed the boiler just carries on heating everything up.
boiler and associated electronics have been checked by the manufactures engineer - OK.
programmer has been changed for new.
the only possibilities left are a 3 way valve and a 2 way valve.
Can anyone offer any advice please

 

[chrishutt]

the only possibilities left are a 3 way valve and a 2 way valve

These are the things one would suspect first of all. The motorised valve micro switches may remain in open position, causing the heating to continue, possibly due to valve or motor fault.

But why have you got a 3 port and a 2 port valve? (Normally there will be either a 3 port or 2 x 2 ports.)

 

[Paul Barker]

One possible reason, if he has unvented cylinder he would have a 2 port valve (required safety feature) additional to the mid position valve. With s plan he wouldn't have needed the extra valve.