my boiler wont shut off

[big baz]

HI, i have a 4 year old worcester bosch greenstar 28i junior combi boiler, when in heating mode the boiler does not cut out and in it just keeps running. thought the problem could be the radio controlled themostat, took it out -no difference, just using the control knob - set it to 4 the radiators are warmish boiler continues to run witout stop starting but not getting any hotter. turn it to 6- radiators nice an hot still not cutting out - rads not getting hotter, back it down to 5 the boiler turns off , when the temp drops the boiler fires up but still does not go off. you can do this all the way back to the lowest setting. i have replaced the primary sensor - did not make any difference. any ideas? hot water works fine.

 

[PuraTherm]

Has the boiler been doing this all along or has it just started doing it this season? Has it been serviced recently? How many rads on the system? Have you added any rads? Sounds like the boiler isn't producing enough heat to push the rads. May want to have an engineer check the delta T on the flow and return. Worst case scenario is the PCB is toast.

 

[big baz]

HI, it started this season, no it has not been serviced ,there are 10 rads.

 

[PuraTherm]

Definately get it serviced. Have the engineer check the PCB and the flow and return tempratures.