Sadly we woke at 6.30am to a very cold house again - the heating should have gone on at 5.30am. After more fiddling with the Salus thermostat, I turned both switches off and then on again on the Salus receiver, and the boiler started working.
The house started to heat up towards our chosen temperature, but then a few hours later it went off again. I re-paired the thermostat, nothing seemed to happen.
I turned the receiver switches off and on and it started to work.
More emails to the installation company who have yet again 'raised a ticket' but could not give any indication when anyone could come.
Apart from when the pressure drops to zero, the hot water is fine. It is just the heating that is unreliable and uncontrollable.