While you wait for answers, we may have found some information which could help you.
Click here for Heater Working Check
Oil fired boiler thermostat?
Greenstar 24Ri boiler, fast flashing - can I reset?
Remove cover off gas boiler?
Vaillant ecotec 831 plus?
Siemens RDJ10RF thermostat problem?
One radiator in a bedroom is always cold?