hot taps turn heating off

[crawforddm]

I recently changed the radiator in the bathroom and ever since, when the heating is on and a hot tap is used, when the tap is turned off the heating goes off?
the radiator may have been pure coincidence but if not i did it like this:
turned boiler to water only, drained radiators from downstairs drain valve, swapped bathroom radiator and did all relevant pipework, refilled system (fill, bleed, fill, bleed, fill), switched boiler back to heating and water, then tested for leaks/operation.
the boiler is a chaffoteaux brittony 80

 

[twgas]

How long does it stay off for, and how do you get it back on?

 

[crawforddm]

thanks for the reply. ive managed to sort it now. it was a sticky diverter valve. ill get it replaced next week