boiler operating on internal stat

[kpp]

halstead boiler with room stat wired in, boiler seems to be operating on internal stat, over riding room stat. have tested room stat, and is working ok calling for heating but boiler working independanly?
any ideas

 

[stevetheplumber]

you say stat is calling but is it shutting of?

 

[kpp]

stat will operate normally when set to 21-22c if set higher boiler cuts out wtih stat still made ,calling for heating

 

[kpp]

boiler still operating on boiler stat, tested both thermistors all ok, cant get heating above 23 c ??