Vokera 20-80RS Flowmatic fault

mulls76 · 11 Jul 2007

Hi all

been out to this boiler today with customer saying the pilot light keeps shutting off at various intervals. I've never worked on this boiler before and there was no MI's present so hopefully someone can help me.
What seems to be happening is that when the pilot is lit the boiler will work ok on a demand for heating or H/W. However it also seems to be firing up and shutting down repeatedly even when there is no demand at all. Obviously this causes the temperature of the boiler to rise as the heat is not being taken away from the boiler and therefore the O/Heat stat kicks in and shuts off the pilot etc. Now the presure is fine and the fan & pump seem to work ok so not sure if this is maybe a stat fault or maybe the P.C.B? Is it normal for this boiler to cycle with no demand for heat?
Hopefully some of you can help me out as I don't like having to scrap perfectly good boilers due to my lack of knowledge!

DP · 11 Jul 2007

What you need to find out is why the pump is running when no demand is in place.

Download MIs from Vokera website.

mulls76 · 11 Jul 2007

Yeah but not only is the pump running but the burner is firing up, staying on for about 30 seconds and then shutting down. It seems to repeat this cycle until eventually the boiler overheats and shuts off the pilot. There is no demand and the water just circulates around the boiler. I'll get the MI's, just wondered if anyone had any prior ideas.

Dan Robinson · 11 Jul 2007

Stuck microswitch?

mulls76 · 11 Jul 2007

Hi Dan, that's one thing that i didn't check. I guess the H/W microswitch could be stuck on. I'll check it and let you know, cheers.

DP · 11 Jul 2007

Mulls you are missing the point of my post. If the pump is running (it is pump run that starts the sequence), then the sequence WILL culminate with burner firing. You cannot have pump run (apart from dispersal of residual heat actioned by CH stat) which will not result in burner firing.

A faulty microswitch could certainly result in burner firing, but the heat generated would be to the radiators, unless there is a second fault resulting in circulation within the boiler. In this case one expects the front panel stat to operate initially, followed by safety stat to disconnect power to gas valve to the put out the pilot at 95 degrees C if all fails.

All above is conjecture as one has to be in front of the boiler to crack the fault.

Dan Robinson · 11 Jul 2007

Would have to agree Danny, but I have seen Flowmatics do strange things...

Agile · 11 Jul 2007

mulls76 said:
I don't like having to scrap perfectly good boilers due to my lack of knowledge!

I am sorry about taking up this point but dont you think that is rather unfair for you to apparently expect the customer to pay ( you ? ) to fit a new boiler just because you lack the skills to repair it?

These are very simple boilers with no microprocessors or even anything complicated just a few microswitches and stats and totally repairable!

Surely if you cannot repair a boiler then you should gracefull bow out and call someone who can?

So many times I come across boilers, some only three years old, which have been replaced just because someone did not have the skill to repair them.

Tony

mulls76 · 11 Jul 2007

Agile that is my point. As i'm obviously not as experienced as some, i'm looking for advice in order to gain experience and therefore be able to fix it. I would rather fix it than just advise the customer to replace it as many other people would because they can't be bothered to learn. I'm sure it's nice for you to have a go at those of us who don't yet have your knowledge, but it's a rather pointless exercise which does little other than allow you to tell everyone how great you are.
Thanks to those who have actually tried to help.

mulls76 · 11 Jul 2007

Thanks for your reply DP. I totally understand what you're saying in relation to the pump running, i'm just not sure why it is running! There is definitely no demand and the boiler is just circulating around itself and not the rads. Would a sticky DHW microswitch cause this scenario? If the hot water tap isn't running then H/W heat exchanger would get too hot eventually leading to O/Heat stat shutdown?

Agile · 11 Jul 2007

I think you have missed the point that I was tring to make and in the course of that ended up being rather unpleasant towards me. The only effect that is likely to have is to make me slightly less likely to help you repair it.

To reiterate, you dont have "to scrap a boiler" just because you cannot repair it. All you need to do is to admit it and call someone who can.

I am quite often called by other RGIs to fix boilers they have failed with. I am happy to come and sort it out and I show them what I am doing and how to diagnose the fault and then fix it. Not only do they get the boiler fixed they get a free lesson as well.

Tony

mulls76 · 11 Jul 2007

Tony, thanks for your reply. I wasn't being unpleasant i'm just looking for some help really in order to gain some of the experience you obviously have. I've lurked around here for quite a while now and have noted you as one of the more knowledgable posters here and so i was a bit disappointed that you took exception to what was really a throw away line at the end of my post. I would always look to repair rather than replace and I was just trying to point out that some people never try very hard to seek the knowledge required to be able to fix faults. Sorry if i've offended you, it just felt like you were having a dig at me really when all i'm trying to do is learn from the masters!

Agile · 12 Jul 2007

I was not having any dig only pointing out the obvious that a boiler should not be changed if its still repairable even if that means calling someone else.

Back to the boiler! If the pump is operating then as Dany said there is a demand for heat. Its unusual but the DHW microswitch is the obvious culprit.

Have you inspected the diverter valve pin? They stick out more often then the microswitch failing?

If the pin is coming out and retracting then have you checked the microswitch properly with a meter?

Tony

mulls76 · 12 Jul 2007

Thanks for your reply Tony. I'll check the diverter pin when i go back. I've got hold of the MI's too so i'll work through that as well, I cant really think of anything else that could cause this particular fault other than a possible pcb problem. If anyone has any more input then I'd be gratefull to hear it.

Thanks

DP · 12 Jul 2007

My input is, how can you assume anything? Carry out a check with appropriate instrument and look for the cause.

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Vokera 20-80RS Flowmatic fault

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