We have a Watchman monitor on our oil tank which has worked well for nearly twenty years now.
Recently, it has been behaving oddly in that the house receiver seems to lose contact with the tank sender, but only from around lunchtime to late afternoon. Early evening, the indoor display suddenly works again, and continues until lunch the following day.
This has been happening for a couple of months, but not on damp, dismal days like today, when the connection is not lost. It cannot be a coincidence that the sun, when shining, is aiming vaguely at the tank from mid day to late afternoon.
However, if it were a low battery at the tank end problem, I would expect the sender to be more powerful, not less, when in the sun, the heat exciting the AA batteries.
There is ivy to one side of the tank, but I cut that back at least twice a year to keep the tank filler and Watchman completely clear.
Any bright ideas?