I was wondering if someone could help please.

I have a Potterton Suprema 40 boiler and today i had the circuit boards replaced on the hot water tank as the water had not been heating up. However, since the heating man came my radiators have been on full, my room thermostat appears to be working and when turning the dial shows it is at 26 degrees.
Previous to this visit the heating had been working fine.

Can anyone help?

I have spoken to the heating man since and explained but he thinks it maybe the room thermostat.