Baxi Duo Tec Combi 24 HE - No heating?

Hi can anyone help me? I have got a Baxi Duo-Tec 24 combi boiler. The boiler seems to be working fine as we have got hot water, but the heating has suddenly stopped coming on.

We have got a separate, remote timer (battery-powered) and I have replaced the batteries and everythig is switched to ON. I have gone through the troubleshooting in the user guide and nothing points to
this error(we get no error code). The boiler doesn't actually come on and radiators are cold. But if I turn the hot tap on everything is fine. The heating and hot water icons are selected on the display and up to today it has
worked fine.

There are no error codes displayed?

Any ideas HELP!!!