Vokera R S20 80 Flowmatic boiler flow switch

Robertpaisley · 27 Aug 2013

I'm puzzled about the correct operation of this flow switch (the one which controls the fan, mounted on the heating manifold).

With everything off, the plunger is out [Seems correct]

In CH mode, the plunger retracts when the pump is running, which I think is correct. [The CH seems to function ok.]

In DHW mode, the plunger doesn't retract when the pump runs. Is this correct? [Burner doesn't light in DHW mode.]

Agile · 27 Aug 2013

As I recall that's the correct operation on that particular model.

Although the normal resting position on most boilers is with the pin in !

Edit, but of course it should also be retracting on DHW as well as on CH. May be a blockage or reduced flow in secondary heat exchanger.

Look at pump impeller to see if its clear and do the finger test.

Tony

45yearsagasman · 27 Aug 2013

The pin should retract in both CH and HW modes. Replace the diaphragm with a new one to start with, and clean and lubricate the pin. Also, if it doesn't go out far enough the fan will not run on low speed and you will get pilot failure.
Check the diaphragm first.

Dan Robinson · 27 Aug 2013

That pin has thrown me more than once.

Vokera Tech support are very good on this model though. I like the challenge of these boilers. Avoiding dropping the million little screws is always fun

DP · 28 Aug 2013

If the plunger does not retract, either air in the system or pump weak.

Robertpaisley · 28 Aug 2013

45yearsagasman said:
The pin should retract in both CH and HW modes. Replace the diaphragm with a new one to start with, and clean and lubricate the pin. Also, if it doesn't go out far enough the fan will not run on low speed and you will get pilot failure.
Check the diaphragm first.

Yes thanks. I'd already replaced the diaphragm, and cleaned an lubricated the pin. Pin was initially stuck in, giving the pilot light failure you mention.

With hindsight, had to be stuck pin, not diaphragm, as the differential pressure on the diaphragm pulls the pin in. Also, could have cleaned and lubricated pin just by removing "O" ring carrier, without delving into the diaphragm.

Next step is to follow up the other suggestions.

DP · 28 Aug 2013

Robert, I would seriously suggest a full service. you can tinker about with it, but you will not have all the bits and bobs I would have to carry out the task.

Good luck anyway.

Robertpaisley · 28 Aug 2013

DP said:
Robert, I would seriously suggest a full service. you can tinker about with it, but you will not have all the bits and bobs I would have to carry out the task.

Good luck anyway.

Agreed. I've PM'd you to ask whether you'd like to take a look.

Dan Robinson · 28 Aug 2013

DP#s is the man with these.

ianmcd · 28 Aug 2013

An old boiler but a decent one in its day, be prepared though that sometimes even replacing the full hydraulic service kit does not solve the problem, does work on about 95% of them though

Agile · 28 Aug 2013

Its his favourite boiler!

Some people still drive Morris Minor 1000s

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Vokera R S20 80 Flowmatic boiler flow switch

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