My daughter has a fairly old fashioned but pretty standard gas CH system which is controlled by a Horstmann H37 controller.
A couple of months ago it stopped working completely, it was blowing the fuse in the wiring box. After a bit of diagnosis with a meter I discovered that the suppresor capacitor in the control box on the boiler had failed. I fixed that (with a proper X rated mains capacitor) and everything worked perfectly again - until now.
Now the controller doesn't turn the boiler off at all, the only way to stop the boiler is to remove power from it (there is a switch to do this).
Is this likely to be simply a programmer fault/failure or are there other possible explanations? The programmer is obsolute so if it is faulty will have to be replaced.