wireless thermostat not triggering boiler?

last winter I had fitted a new boiler. They also put in a wireless thermostat. It worked fine and hten I turned off the central heating through the summer.

I've now tried to put the central heating back on. It seemed like the thermostat and it's receiver were having problems communicating so I put in new batteries and also tried to make them relearn. I think I eventually managed that but my thermostat is showing that it's sending the message that heat is needed, the timer bit is showing as heat being on but the boiler is not sending any hot water to the radiators.

Any ideas?