Potterton Netaheat 16-22

[ChrisR]

"So I assume SG1 must be the trigger to light the pilot?? "
Yes it makes sparks which light the pilot, which is then detected electronically (it produces a small rectified current)

"Input terminal where?"
Not obvious is it.
But it WAS working so that should be OK.
The spark may be going somehwere other than where it should, or the detection side may need attention. Corgi time.

 

[pixey]

Is it possable that the electrode is not detecting the heat from the pilot, although the end is clearly getting hot, and so the main burner won't light?

Is SG1 still trying to light the already lit pilot?

I won't take the main cover off the boiler, but I don't want to be billed for a faulty part that is not actually faulty when I do get someone in.

So any help I can get in identifying the faulty part are very much appreciated.

P

 

[Agile]

Although I suggested it must be a model with a PCB, as you suggest it MUST be a model with the PCB otherwise it will not have the spark gap which he could not recognise.

So the fault is a failure to detect the pilot flame, more likely to be a PCB in my thankfully limited experience of these dreadful to work on models.

Thank goodness they are usually reliable!

Regards

Tony

 

[kevplumb]

change the spark electrode

 

[ChrisR]

You mean get a corgi to change the spark electrode?

Tony yes - in a sense they all have pcb's because the spark generator is in a module which presumably has one. (Or were they still using tag strips?)

Hong on a mo then we're looking at a Profile in waiting - and there's a prcedure for testing the flame rectification...
LGSRS call.

 

[Dick n Dom]

Caller...Next time you have the bottom case off please let this forum know the G.C number (Gas Council) this will help identify which particilluar model it is..Is there any sign of a mercury vapour switch on your model or in any paperwork you have.

 

[pixey]

Caller...Next time you have the bottom case off please let this forum know the G.C number (Gas Council) this will help identify which particilluar model it is..Is there any sign of a mercury vapour switch on your model or in any paperwork you have.

The GC no. is: 41 601 66


I have only been in this house a short while and amongst the boiler found a reciept from when the boiler was last inspected, and it quotes the electrode and wire as being replaced 13 months ago.

When you look very closely through the pilot flame, you can see the spark for the pilot in time with the flashing of the spark gap.

What actually detects the pilot is lit on this boiler, because it really looks as though the fault may lie there.


Thanks Paul

 

[Dick n Dom]

As already been said on this forum...Replace the control board.

 

[pixey]

As already been said on this forum...Replace the control board.

OK I will price one up locally, do you know what or how this boiler senses when the pilot is lit, though.

paul

 

[kevplumb]

it senses through the SPARK ELECTRODE change it first
lot cheaper than a board

 

[Agile]

The spark gap has to be changed by a CORGI because the burner has to be removed to get it off.

The spark electrode also acts as a flame detection element. The earthy side of the EHT transformer is not taken directly to earth. It has a small AC voltage applied to it. This earthy end is connected via some high value resisters of a meg or so to a DC detection circuit which serves to detect a flame and enable the second stage of the gas valve and to turn off the spark generator.

A flame contains isonised gas and this conducts the applied AC to earth. However because the gas is leaving the burner at quite a high velocity the effect is to conduct more for one polarity than the other and results in a DC offset to the applied AC voltage. Its called flame rectification! This DC is detected as described in the previous paragraph.

Got it?

Tony Glazier

 

[ChrisR]

I checked - the procedure for measuring the flame current is documented but you'd be looking for a current of around 1.5 micro amps through the spark electrode. Not a very good idea though while it's still sparking!

 

[pixey]

I checked - the procedure for measuring the flame current is documented but you'd be looking for a current of around 1.5 micro amps through the spark electrode. Not a very good idea though while it's still sparking!

Couldn't I test this current by inserting a digital ammeter in the enectrode lead and then powering up?

Paul

 

[pixey]

BTW, thanks Tony for your good answer.

 

[pixey]

I removed the relay from the cct board, as it seems to be the only moving part, carefully removed the cover so I could see which pins were connected to the coil, and found that the coil is open cct!

I re-soldered the relay back into the board, powered up the boiler, manually operated the relay at the point it should operate, and bingo, main burner lights.
MAGIC.........
Now I can get a new cct board knowing that it will work, or perhaps just a replacement relay, if I can find one.

If anyone knows where I can get the relay from it would be great, the numbers on it are: 111C DO 36 - 18, and on a sticker:963463 1022.

Thanks very much to everyone who has helped me to localize and prove this fault. It is very much appreciated.

And all without removing the main cover.

Thanks.

Paul