Ok, for clarity to the OP who we are supposed to be helping (rather than getting Pedantic with each other)
“Based on the age of the house it is unlikely to have cavity wall insulation “
As I said in my reply DO address draughts and DO ignore people telling you that there is little heat loss through the floor, we are looking comfort levels and by insulating under the ceiling you are producing a bedroom floor at closer to ambient temperature rather than at closer to outside...
Some good replies along the right lines, we are all advising without seeing the property, if you say that the garage is at least 65 years old the house isn’t going to have cavity walls.
For the bedroom address the floor, ignore anyone saying that the floor isn’t losing much heat. We are looking...
It strikes me that if tony had put the effort in he might have been able to help rather than just come up with negative vibes. I hate people who go around looking for reasons not to do something.
I wish I had the skills to answer, but as you've drawn a blank here try the technical help line...
Bit late to reply, but in case it helps anyone else searching. Often the reciever is too close to the electronics of the boiler and this is where the interference comes from.