Just to add.
Some diverter valves have a motor that moves them following a command from the pcb (originated by a flow sensor of some sort)
Others have a rubber diaphragm that is sucked by the venturi action of a single tube or the differential pressure action of two tubes which moves it. A spring holds it in the opposite position.
Then there was a way of doing it with wax capsules but hopefully that is a thing of the past.
Flow sensing is usually by mechanical movement of a push rod or similar against a microswitch, but Biasi do one that senses flow with something called a hall effect sensor which senses proximity of a magnetic field, flow of water sends a magnetic shuttle towards the hall effect sensor. I think the shuttle gets stuck due to dirty water.
Diaphragms weaken or get torn (or get held off their seat by debris preventing proper suction, motors wear out or the plastic cogs and wheels which converts their power to the moving part of the diverter valve wear or spring apart uninvited, and the moving parts inside the diverter valve get stuck, wax capsules get old and don't work.
Some boilers sense flow with a ball on a vertical length of run that gets forced up against gravity and I think a reed switch.
Then there is a turbo flow sensor, I haven't pulled one apart but basically a turbine spins round and generates a current I suppose.
A very reliable method of sensing primary flow is by monitoring the temperature sensors, if they alter at the expected rate the pump must be working.
I think the turbo flow sensor for hot water and thermistor monitoring for primary is the best of both worlds, and a motorised diverter valve.
mechanical parts eventually fail usually intermittently making it hard to diagnose, you have rpeat sometimes 150 times to prove the faulty part, even then it will mainly only do it again as you are doing the three point turn in your van, you get a phone call back, try another 150 times and it still won't do it for you. You have to know the boiler, know the weak links, change those as a matter of course and hope you don't get a call back in such situations.
Come on here, ask "these things are hapening on a Genesis any ideas lads?" most people will say walk away, but someone might have a handy past experience of the same symptoms.
Most problems are external to the pcb because the moving parts out in the environment of the boiler have a harder life. BUT pcb's can get wet, you might wet it and cause a second fault, my wife's hair dryer has saved me a few times, and my soldering iron to resoulder dodgy looking joints while I was there. The moving parts on pcb's (relays) can fail as much as the component they operate, or the movement of them can cause the pins to formn a dry joint and simply resoldering them can fix the thing. Unless familiar with and maybe qualified to an extend in electronics new pcb. Many on here will tell you not to touch pcb, anything you do that leads to death wil result in you standing in the showers with your back to the wall hiding the soap wandering how you are going to persuade the judge you were suitably qualified to change a part on the pcb. If he isn't satisfied with your qualifications it's time to make friends with some big guys who can protect you from some other big guys that have a yearning for something you can proivde fpr them willingly or not.
