combi microswitches

Hi all.
I have a few questions on combi boiler.
Generally speaking, without going into boilers makes
1) what is the function of the secondary flow switch? I mean what component does it send the signal to when calling for HW?
2)what is the function of primary flow switch? Again, what component does it send the signal to and when?
3)I understand that when calling for HW the divertor valve moves and makes a micro switch. Again, where does it send the signal to?
4) Are the divertor valve micro switches and secondary flow switch the same thing?
I know there are quite a few very knowledgeable people on this forum who might be able to clarify these few points.
Thanks in advance for your time.

Generally being the operative word

1 See '4' Follow the wires! generally the pcb to indicate that water is flowing through that component and that the ignition sequence is to be started

2 Follow the wires! generally the pcb to indicate that water is flowing through that component in this case indicating that the primary circuit [CH] water is flowing and that the ign sequence can be started when all other requirements are met.

3 See '4' but be careful. Some DVs have 2 microswitches in them

4 Generally speaking yes. It normally indicates that there's a call for hot water[DHW]. I rarely use the term secondary flow switch and there could be a boiler out there somewhere that works differently.

It's best to be specific as there are so many ways to indicate if water is flowing through a given pipe and create a useable signal. Get the MI's for the boiler in question and read them thoroughly.

When I was a young Sluglet my bedtime reading material [apart from porn, lol and the readers digest DIY manual] was a Haynes manual which I used to read over and over until I learnt how each component of an Austin 1800 worked. It was easy then to see how different manufacturers got over the same problems as I moved on.

If you want to do the same with combi's then thats a good way to do it. Reading the manufacturers instructions for just one combi over and over until it sinks in, then take the rest in your stride learning the different ways of doing the same job as you go. The sequence of events usually found in the MI's helps put together what order the parts work once you have figured out the function of each component

I hope that helps you with your homework

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.

Not much I can add to that, except that the middle-aged Vokera manuals were very good at explaining how things worked, so would be good to start with.
Also the old Flowmatic shows the circuit on the pcb, which is pretty simple, so you can work out the sequence on there.
Later boilers have fewer switches, using the processor on the pcb to do similar things.

ChrisR said:

Not much I can add to that, except that the middle-aged Vokera manuals were very good at explaining how things worked, so would be good to start with.
Also the old Flowmatic shows the circuit on the pcb, which is pretty simple, so you can work out the sequence on there.
Later boilers have fewer switches, using the processor on the pcb to do similar things.

Click to expand...

Thank you all 4 your inputs guys.