Vokera EXCELL 80SP Burner going on and off when DHW on

MacD · 11 Sep 2007

I have a Vokera EXCELL 80SP and when DHW is turned on the burner lights for about 30 seconds then goes off for about the same then back on again and so on. The central heating is working ok but again if DHW turned on the burner goes on and off.

Have had a CORGI engineer to it he has used a seal kit, replaced the Domestic diaphragm and diverter valve seals and checked the valve. The fulcrum arm and micro switch all seem to be operating ok. I am looking for advice as to what else should be looked at.

Just another point, when the outer cover is off the boiler I have noticed the burner front cover plate and all the metalwork in the boiler (pipes etc.) is very hot even when the boiler isn't operating and just the pilot light is on, is this normal?

MarkBarl · 11 Sep 2007

Just had my 80sp replaced, but over the years I had seen similar problems. Have a look at the temperature gauge. When the boiler is on DHW mode it burns with a bigger flame assuming that the additional heat is being removed when it passes through the DHW heat exchanger. If there is a flow restriction through the Main heat exchanger and DHW heat exchanger the water in the system will get too hot and the boiler will automatically shut off the burner until it cools down. This is much more noticeable when delivering hot water than heating as the circuit that the water is traveling through is much shorter. If this is the case, the temperature gauge should show it getting too hot. It may be that your heat exchangers have become scaled up or blocked with sediment.

nickso · 11 Sep 2007

the above is a possibilty among others.

probably more likely is the air pressure switch is faulty or the fan/venturi are blocked. i would wager that if you took the combustion chamber cover off it would run normally. a sure sign of a blockage or lack of air pressure due to the fan impeller being blocked.

MacD · 11 Sep 2007

Thanks for your suggestions. Unfortunately my temperature gauge isn't working at the moment!

I took the combustion chamber cover off but the burner still kept going out. One thing I did notice while the covers were off is that the fan wasn't moving when the boiler was idle but did come on when boiler ignited.

nickso · 11 Sep 2007

MacD said:
Thanks for your suggestions. Unfortunately my temperature gauge isn't working at the moment!

I took the combustion chamber cover off but the burner still kept going out. One thing I did notice while the covers were off is that the fan wasn't moving when the boiler was idle but did come on when boiler ignited.

stuck flow switch will stop the low speed on the fan working.

still think its a fan/venturi/aps problem but its difficult to say without seeing it.

has it been serviced? a proper service goes a long way on these.

MacD · 11 Sep 2007

Boiler hasn't had an in depth service just the basic "clean it".

Some more info I have is I think the boiler is "kettling" just before it goes out and the central heating out flow pipe is getting hot even when the boiler is set to DHW mode only

DP · 11 Sep 2007

Your HW heat exchanger is blocked!!

MacD · 11 Sep 2007

Thanks DP I will look into that as I know your advice has always been good here.

MacD · 11 Sep 2007

I have solved the fan not working at slow speed, there was a loose wire on the Fan Resistor. This has also solved the other point I brought up in my original post about all the metalwork in the boiler being hot, it has now all cooled off with the fan now running at slow speed.

diynot

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Vokera EXCELL 80SP Burner going on and off when DHW on

Similar threads