Worcester 28i Junior Combi... Hot water but NO Heating ???

Hi everyone,
We have a Worcester 28i Junior Combi which developed a fault this week. We have hot water fine but no heating. This same fault developed when we first moved into the house 2 years ago, it was the heat exchanger. (The boiler had not been used for at least 6 months before that as was an empty property) Replaced by British Gas for £99 plus min 12 homecare package. All been fine since. However the batteries died on the wireless room stat last week and since then have had no heating.
I dont know whether this is just a coincidence or linked to the fault, as although the batteries have been replaced and the clock working ok on it, nothing from the boiler. Does the room start have to be "paired" to the boiler again ? any suggestion on procedure ?
The only time we can get any heating is if we press the "spanner" maintenance button for 10+ seconds and it fires into life with red hot heating for less than half an hour... then shuts down again !!!!
Spoke to BG, explaining the situation (we cancelled the contract last summer as all was fine and were having new pipework installed throughout house so no heating at all obviously needed over the summer), advised new contract £22 pm as known fault plus one off repair cost.
Any other suggestions or advice gratefully received before i make another investment to them!!!
Regards
Dave
Maidstone, Kent