I'm hoping someone can help.
We had to drain the cold water tank in the loft to replace a toilet siphon. That is all fixed and we refilled the tank and found we were getting no hot water from the hot taps. Worked out it was an air lock which we've fixed by blasting mains pressure water up the hot tap.
However, now whenever the hot water system comes on ALL of our radiators are coming on. The heating is switched off.
Has anyone got any ideas what this is and how to fix it?