Heating Woes

[Banshee]

Having some problems with our heating at home at the moment and due to my inherent nature of not trusting anyone else I'm determined to fix this myself as I refuse to believe it's anything difficult.

We live in 2 year old property with an Ideal Logic ESP 35 Combi Boiler in the kitchen, it provides all of the hot water from the taps and controlling the heating we have two Danfoss TP5000SI Thermostats one for the downstairs heating and another in the master bedroom for the upstairs heating.

We started getting an issue with one of the radiators not heating up in the study upstairs where the girlfriend is working from home at the moment so myself and my brother did a bleed of the system and turned all the heating on and shut the valves on the radiators downstairs which seemed to sort everything out for a week or so.

We have now lost ALL heating upstairs and following the same procedure as before suspecting it was the same issue, we bled all of the radiators again but this time with no effect. My brother was fairly confident that we had airlocked the system so we drained the system fully last night via the radiator closest to the boiler in the kitchen with a hose out the back door, we then opened up all of the bleed valves on each radiator, balanced the system and then re-filled the system and bled again. We weren't able to force any air out of the system at all and got a clear stream of water from every radiator and towel rail

The heating downstairs works fine and as soon as you manually flick the temp up past the ambient temp on the stat, you get the audible click from it and almost instantly, the boiler will kick into life and a few mins later, hot rads.

We do not get the same upstairs, we get the audible click from the stat again but the boiler just does not respond no matter how long we leave it on.

We're a little confused by this as now it appears that we have had two separate issues

I'm thinking that the stat must now be at fault as it isn't communicating with the boiler I've read that there is a wireless version of my stat which we def don't have, our appears to be the hard wired version.

I'm out of ideas and hoping you boys might be able to advise a few things that I may not have thought of yet.......

My plan of action this eve is to get home and swap the stats around thus proving if that is where the fault lies If that is the case I'll be a happy chappy as they are only £40 on Amazon

Please help!!! Her indoors is FREEZING