To expect my central heating to work

[WildwestWind]

Plea for advice. Lots of snow here so have the heating on all day. Changed the boiler controls from timed to on and turned up the thermostat in the hall.
Heating comes on, house gets warm, then heating switches off and house gets cold. Went and had a bath and it appears that running hot water makes heating come on again. Any ideas what's wrong?

Anyone?

Maybe the pressure in the boiler? I don't know how though. Google the boiler and see if you can find an answer. Is it a combi? Can you set the timer for the hot water without changing the heating setting, that might help?

I have wasted a fair bit of my life in the last 2 weeks raising the boiler pressure as the heating goes off when it drops to a certain level, and then having to bleed the radiators to get it to drop because it filled too much. I get hot water out of the cold tap before it turns cold.