Glow Worm Ultimate 30 C hot water but no heating.

[Thedaddy71]

Hi everyone, hope you're all well and hopefully someone will be able to help with a problem I have. The boiler seems to fire up with heating no problem at the start of a program but will randomly stop heating. There are no error codes on the boiler and the thermostat (Climapro 2RF) shows no signs of any issues, I have also replaced the batteries in this. Hot water is working fine. The radiator symbol on the boiler is flashing as expected and I can control the boiler from the Climapro so it doesn't seem to be this.
The problem started Xmas eve so any help would be greatly appreciated.

Many thanks.