We have a Honeywell Smartfit controller which keeps crashing showing code F4 on the timer. F4 is 3-port valve stuck but the valve and actuator seem all right. Google suggests this is a common problem and the solution is to replace the controller.
First question is, has anyone managed to get a free replacement out of Honeywell?
Failing that, can I replace it by a different make? Can I just connect up the boiler, valve and timer the same way or would I need a new timer?
Is it even possible to DIY a controller, e.g. given a microcontroller board and some relays? Being able to fine-tune the heating program would be great.