Well I am not a central heating engineer, but I have dabbled with my 105E instant combi,and Have not as yet resolved the problem except at the moment out of the blue it started giving me CH and the radiator led lit of course. I have had this before though, and it was intermittent.
Anyhow I checked both the HW and CH temperature sensors with a test meter (system powered down of course), and both were okay with a resistance reading of just over 10 K ohms when cold, which drops to a low resistance as they warm up. I also changed the main circuit board, and did the obvious like disconnecting my room stat from the AC input panel contacts 1, and 2, and putting a wire link across. None of these things has cured it. The system pressure is okay at 1.5 thereabouts. ZAD had this problem back in May exactly the same, I mailed him to see if he resolved it but had no reply as yet. If he did resolve it I will post it here.
Cheers DDSK.
Anyhow I checked both the HW and CH temperature sensors with a test meter (system powered down of course), and both were okay with a resistance reading of just over 10 K ohms when cold, which drops to a low resistance as they warm up. I also changed the main circuit board, and did the obvious like disconnecting my room stat from the AC input panel contacts 1, and 2, and putting a wire link across. None of these things has cured it. The system pressure is okay at 1.5 thereabouts. ZAD had this problem back in May exactly the same, I mailed him to see if he resolved it but had no reply as yet. If he did resolve it I will post it here.
Cheers DDSK.