Wind down CH boiler powered flue problem

johnjory · 7 Aug 2006

I have a Vokera 20-80 RS Flowmatic combi boiler.

The flue has been put in an exposed position so that when the wind blows directly into the flue the boiler will not ignite. I guess the wind pressure is preventing the flue flow diaphragm switch from making.

Phoned Vokera, they just said 'get somebody round to look at it'.

Does anybody know of a wind shield that can be fitted.

Thankyou

John Jory

Agile · 7 Aug 2006

Can you described how the flue is fitted?

That kind of boiler should have no problem with external wind.

I suspect the problem is due to a partial fault and may result from not being properly serviced.

You must NOT try to fit any flue shield unless its at least 500 mm away and then only under the guidance of a CORGI engineer.

In any case I dont think its necessary if the underlying fault is addressed.

Tony

johnjory · 7 Aug 2006

Tony, thank you for immediate reply.

Flue comed through the wall horizontally and has a wire cage over it. Looks totally normal to me.

Boiler has been serviced. It was this service that discovered that the microswitch on flue flow detection diaphragm had been disabled. A new diaphragm was fitted. The new ones cannot be adjusted like the old ones could. It is since then the problem has ocurred. This is what made me suspect the sensitivity of the flue flow diaphragm.

Thanks for your helpful suggestion about distances for any shield arrangement.

John Jory

Agile · 7 Aug 2006

The person who serviced your boiler should have been reported to CORGI if he is indeed registered if he left it with a bypassed switch!

It is a very strict safety fact that you do not leave any boiler operating with a safety device bypassed!

The original manufacturer's part are usually sealed at the set operating point. Its not really correct but some engineers do carry adjustable switches and set them for the boiler in question as that means they can cover a wide range of spare parts.

If he did the right thing and replaced it with the correct preset part then its likely to be another part which requires cleaning. He should have known about that but he might have just been lazy!

Tony Glazier

DP · 7 Aug 2006

It has NOTHING to do with the flow switch.

Sequence of operation is Pump on, Flow switch operate and then fan goes to high speed. Also there is no adjustment on the flow switch or the flow manifold.

What you got is a service that is not a service. The problem, I am 99% sure, is service related which was not picked up when the boiler was looked at.

Does the boiler not work correctly on a calm day to start shutting down when the wind velocity is high across the flue? Is the boiler noisy when it is working? A yes for each would mean getting the man back to have another look at it. If he is telling you there is an adjustment on the flow manifold that is something I must be missing.

johnjory · 7 Aug 2006

Tony,

Thanks again for helpful reply. Naturally when it was discovered that such an inportant safety device had been bypassed, I had it rectified without question. No chance of reporting to CORGI, he is long gone! The nature of the fault is such that it did not occur for months, until the wind was in the right direction.

When you say, "...then its likely to be another part which requires cleaning...." Do you have any suggestio as to what part might possibly need looking at?

Thanks again
John Jory

scatmanjohn · 7 Aug 2006

I believe he is refering to the fan venturi.

johnjory · 7 Aug 2006

Dear DP

Thanks for your helpful suggestion also.

To answer your questions .."Does the boiler not work correctly on a calm day to start shutting down when the wind velocity is high across the flue?" A: Works correctly on calm days and on windy days. EXCEPT when wind blows directly into the flue.... "Is the boiler noisy when it is working?" A: No.

Your point about sequence of operation is interesting. Pump comes on OK . Then I think fan goes to high. If this is indeed the case, it must mean that the flow switch has operated. This would support your suggestion that it has nothing to do with the flow switch.

Given it is an intermittent fault i.e it works OK until the wind is in a particular direction. It makes fault near impossible to diagnose until it is actually present.

Any suggestion as to what else it might be would be welcome.

Thank you
John Jory

johnjory · 7 Aug 2006

Dear Scatmanjohn

Many thanks for that.

From the posts, I was beginning to think it might be the fan efficiency.

What is the process of cleaning out the fan venturi? Or is it a matter of replacing the assembly?

Thanks
John Jory

Agile · 8 Aug 2006

You have now ventured into the territory of CORGI registered engineers.

As I do not hide my identity, I do not give any advice on matters relating to safety issues which require a certain level of competence.

The fan and venturi fall into this category.

After many years of operation the fan impeller can become heavily laden with dirt and washing this off will often cure these problems. This is rarely cleaned on a service ( except for DP ).

Tony

johnjory · 8 Aug 2006

Tony,

The careful qualifications contained in your post are noted.

I've already had a look at the fan assembly, and it looks pretty dirty. I posess a reasonable level of electromechanical skill & ability and cleaning the impeller/venturi does not look too much like rocket science. So on my head be it!!

Thank you again. I'll let you know how I get on next time there is an east wind in Norwich.

John Jory

johnjory · 8 Aug 2006

Gentlemen,

Subject strictly to my ".......on my head be it...." caveat above.

Found the impeller rotor blades to be caked with dirt, cleaned this all off. This must improve efficiency.

Also cleaned venturi with a pipe cleaner. With regard to its 'hammer' shape with air entry points top & bottom, can now see reason for comment, "......that.. boiler should have no problem with external wind."

Boiler seemed to fire up a little quicker than before and, whilst not previously exessively noisy, now seems a little quieter. This suggests to me that impeller rotor is now more balanced.

All that seems to suggest that something positive has happened. But will only know for sure next time there is a brisk easterly wind in Norwich!!

I owe you all a beer in any case.

Many thanks
John Jory

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Wind down CH boiler powered flue problem

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