Ideal icos condensing boiler-Heat only works with water on

Ideal icos condensing boiler. We got home yesterday post Christmas to discover a very cold house. Pre holiday I set heating to come on overnight only. We switched heating from timed to continuous but it didn't come on. Screen said 0 and boiler light was off. However, when I switched hot water to continuous the ignition light lit up and screen said C and both came on. The heating now only comes on if hot water is. Any ideas? I've tried reset and switching off and on! Just wondered if there's anything I can do or if we need to call someone out! We don't have gas appliances so can't be sure if working ok! Thank you

The fault is not on the boiler but on the external controls.
Probably a motorised valve.

Thanks for your reply. Who would I need to resolve that? The boiler man or someone different? Thank you!

Boiler man or plumbèr could fix this problem. Sounds like a faulty zone valve