The H72 error code usually means your thermostat has lost power, but you're saying it is in fact powered on? Is your thermostat on a stand or wall mounted?
If your thermostat is on a stand
I know it may sound obvious, but make sure that the power cable is fully inserted into the power plug and that the plug has been pushed all the way into the wall socket. I would also check that the wall socket is switched on. You can also double-check that the socket is delivering power by plugging in a lamp or other electronic device and turning it on.
If your thermostat is on the wall
Make sure that the thermostat display is completely attached to the base. If it’s not, push it down on the base as you should hear it click. You can also try moving the Heat Link.
- Before you move the Heat Link, turn off all power to your home at the fuse box.
- Move the Heat Link so that it is at least 30 cm away from the boiler or other large metal objects.
- Also, check that there isn’t anything directly between your Heat Link and thermostat, like a large mirror or refrigerator.
- After you move the Heat Link, turn the power to your system back on.
