Ionisation electrode

[Man at B&Q]

I'd like to see you make it work without the flame.

MBQ

[Andy Burns]

It's not something I claim to have known about before geoff mentioned it, but it encouraged a bit of googling ...

It seems it stems from the burning of gas ionising it, so you've got some free electrons available, if you try to pass A/C between the base of the flame and the tip, it'll happen more readily in one direction than the other, you detect the conduction varying with the phase (rather than just conduction itself, or lack of it).

On the other hand, what's wrong with a thermocouple?

[Tim+]

Ask anyone whose boiler won't light on Christmas Eve. ;-).

Tim

[Dave Plowman (News)]

Thermocouple failure is one of the most common things to stop a boiler working, IMHO. At least in my case just cleaning the electrode (or more likely the insulator) got it working, which is a bit cheaper. And it's rather easier to remove/replace.

[harry]

When boilers became efficient they needed fans to push the combustion gas out because there was no convection. They also had no pilot light and had to be lit every time they fired.

The danger was that the gas valve might pass gas and on ignition, the boiler would be full of gas and explode. This couldn't happen when there was a permanent pilot light as any gas leak would be quietly burned off. So the boiler has to be purged (with air)on start up to clear any gas. The ionisation detector detects the flame. If there isn't one when there should be, the boiler goes to lockout. (And gas is cut off) The detector is tested before start up on every occasion and can only fail "safe".

[dennis]

There are many ways to ionise the air/gas.

[Andy Burns]

I've got a spare ... might take me until Boxing Day to find it though...

[polygonum]

You name is drivel - AACMFP!

(Who else has a spare boiler?)

[Andy Champ]

Read it again. If he can't find it until Boxing Day I rather think he means a thermocouple, not a whole boiler!

Andy

[polygonum]

I thought it might be hidden behind the hacksaws.

[geoff]

Sorry - was out till after midnight SCUBA diving last night

looks like andy posted an article that gives adequate explanation

[Tim Lamb]

In message , geoff writes

I read it as implying that the detectable imbalance in current flow was due to size choices for the electrodes rather than ions only flowing in one direction.

I could easily be mistaken:-)

[Man at B&Q]

The way I see it, it also depends on the electrodes. A flame wil not rectify just by being a flame.

MBQ

[Man at B&Q]

Which one would you recomend for a domestic boiler?

MBQ

[Andy Burns]

Well I suppose just letting it squirt out of the jets would rip a few electrons from the gas, though not much compared to burning it.

[dennis]

50 MW plasma arc, or a very fast angle grinder.

[Man at B&Q]

You will need some car body filler to hold those in place.

MBQ