Boiler fires when timer and stat off

[1956]

Daughter moved into house 6 months ago when recently switched heating off noticed rads still get hot. Hot water tank ok. I disconnected timer and room stat and boiler still fired. Also the single port valve for the heating is on the return pipe?
Ariston micro system G.C.N: 41-116-05 hope that's the model number

Any ideas please.

 

[dcawkwell]

2 port valve fault.

 

[1956]

Thanks, I'll take a look.

Is it normal for valve to be on the return to boiler?

 

[1956]

It was a faulty 2 port valve. Thanks