Neta heat / Potterton 10/16 boiler cycling?

[T i m]

Hi All,

Some good friends asked me if I knew any good heating engineers and pre passing any names on thought I'd have a quick look at it myself (I had helped them change the blower in it a few months ago).

It goes like this ..

Power on, fan spins (good blast of air outside) .. 30 sec later gas control solenoid pulls in (presumably 'pilot stage?) and electronic igniter tries to fire up the pilot. After a few tries (it's always been like that apparently) the pilot lights but immediately (.75 sec) goes out with a loud sort double clunk from the main gas valve and the cycle repeats.

I've checked all the obvious (air pressure / flow? valve switching over, wire all intact, pipe all in place etc) and am about to get / fit a new HT lead as I thought I heard it arching out somewhere and also though it was part of the flame failure detection cct (and hopefully it's cheap) but I don't feel confident it is that?

Failing that (ouch) then could it be the electronic igniter / pilot control box doodad (407676 / £100, I've checked the back of that for dry joints and it looks ok) or what else please?

All the best ..

T i m

[Peter Andrews]

do an exchange control board for £30 + VAT

• delivery. No connection with company but my Neta Heat failed yesterday :-( so I was looking for spares today. It's now working for no apparent reason but will undoubtably stop again when it gets colder. I have a manual with a fault finding chart that I could copy if you want. Please reply through group as my email doesn't work anymore.

Peter

[adder1969]

Hmmm 3/4 of a second isn't enough for the "thermocouple" to react so I'm not sure what to suggest really. On mine it was fairly easy to check and/or hardwire all the sensor inputs to both give some supervised heating and also to see where the problem was. for me it was the themrocouple whcih was actually a mercury vapour switch and usually a second or two to react. I got mine from america new for =A315 when they were otherwise =A3100 in the UK.

So, boiler on, control calls for heat, fan blows/sucks which I guess then allows the pilot to open and the ignitor to spark, pilot lights then something goes wrong. So what's the next step in that process? Boiler temp input? High stat input? ..or do they come at the beginning?

[T i m]

That's a good price for what I assume would be a guaranteed unit Peter. Especially if it's to find out that it's not that?

Oh. Doh, of course .. it's getting cold isn't it! ;-(

Ah, that's just a trap so you don't continue fault finding again ...

Ok, that could be handy Peter. A mate has found a control unit in his van (only after I mentioned "shame we don't know someone who had just pulled one of these boilers out and has a known working one .." (though he can't remember if it was good or bad)) and I'm going to pick it up tonight and see what happens. If it doesn't work I might be onto you again for the info (thanks).

All the best ..

T i m

p.s. my email is good.

[cynic]

Check the ignition lead forms a low resistance dc path from electrode to control box. A break will jump the spark but not register the flame presence

[T i m]

I don't think this design uses a 'thermocouple' as in what I'm used to (a probe sticking into the pilot flame) but some for of 'sensing' between the igniter lead and using a side effect of the pilot flame to 'sense' if it's lit or not.

I had thought of doing similar but without any idea what goes on in the control unit (and therefore the in / output logic) I didn't want to make anything worse.

I changed a std thermocouple in my Mum's boiler a while ago and it was under a tenner.

Yup, spot on ;-)

Well, I think what should have happened is after each spark is it checks to see if there is a pilot flame and if there is it opens the main gas valve to the burner (inverter flame detection). I believe it does that using the same lead as it uses for ignition to ground?

Currently calling for both heating and water and boiler stat is working (tested).

Not sure, I would assume the high limit stat (thermocouple?) would just cut the gas off somewhere (being a safety rather than std 'regulation' thing)?

Strangely though, we rang a relative of theirs who had just been through similar, he had bought a new control unit and found it no better. Called a heating engineer in who diagnosed a low gas pressure setting (not sure what / where), suggesting that it had never been installed properly in the first place but had been working fine for the last 3 years?

All the best ..

T i m

[T i m]

Hmmm, I've just replaced the ht lead and sparker probe (£10 minimum order at the local place) but no difference (but cheap things to swap out at the beginning)?

I didn't measure the probs resistance to earth (but still can) but guess if a new lead didn't fix it then it's back to the control unit?

'If' the spare control unit my mate has unearthed works I might be tempted to pop the top off the old one and see if there is anything obvious that could be replaced?

All the best ..

T i m

[adder1969]

If the control unit is very simple it will just switch open the gas valves and it's usually easy to bypass the controller so that happens if you're desperate for some heat and hot water. You just need the fan and the flame (and the pump) and away you go. It's no fun hurrying to fix a boiler in a cold house so I usually get the house nice and toasty first before actually fixing stuff. ...although having said that some people frown at an open boiler with a few wires hanging out of it :-)

[T i m]

They also probably feel the same about a live PC just sitting uncased on the bench ;-)

I did say the boiler seemed to be running ok with the 'replacement' control unit, well it was as of midnight last night at least.

This morning I got a phone call saying the boiler was now 'not working again'. ;-(

A quick look showed that the boiler was indeed 'dead', as in it now does nothing at all?

They had to go out (more chemotherapy for him) and when they come back I'll have probe about and find out where all the power has gone (the controller suggests the system has power but the isolator on the boiler isn't an illuminated one so I can't tell if power is getting down there or not).

It may well just be the 20mm / 1A fuse on the controller has blown (as they can sometimes do for no *apparent* reason) so I'll see how long a replacement fuse lasts. If it runs ok I might measure the current with the DMM and see how near the 1A it actually is?

Ho hum .. back into the frying pan .. ;-)

All the best ..

T i m

[Ed Sirett]

The Electronics module is the same as the Pott. Profile boilers.

One low tech possibility is that as soon as the main gas lights the pilot flame is diverted a little and the flame failure immediately stops the main gas valve.

[T i m]

Ok, so another avenue for a spare ;-)

I was looking at that carefully as it lights and indeed considered it a possibility but as the replacement module seems to have cured the problem (fingers still crossed) I guess it couldn't have been that (unless it was marginal and the replacement module is less 'touchy')?

All the best ..

T i m