Potterton Netaheat flame goes out...

[Dave Ramage]

Hello...hopefully someone may be able to diagnose this boiler problem:

I have a Potterton Netaheat 16/22- probably about 15 years old. Its been running fine for hot water over the summer, and for the last 2 weeks of central heating as well, but a few days ago it developed this problem:

-Turn heating and/or hot water on at the timer

-Valves (S-type layout?- 2* 2-way valves) and pump appear to work OK

-Pilot, then main flame lights and everything runs OK for 2-5 minutes

-Flame goes out and there is a continuous loud clicking sound coming from the boiler. The pilot re-lights after the first click, but fades and eventualy goes out as the clicking continues. The main flame never comes back.

-The clicking carries on until I switch off the heating or water timer control (after about 30 seconds as I don't want anything to blow up!)

-Waiting a few minutes and then switching the heating or water on again results in a repeat of the same process.

Is this likely to be a repair I could do myself, or should I just get a new boiler?

Many thanks, Dave

[IMM]

One version of the neataheat had a plug in relay. It sounds as if this has failed. have a look it is quite large. Check it out. Some time you can see it arcing. If it has failed go to Maplin and buy one the same. The makers charge more for a standard common relay you can buy anywhere..

[BigWallop]

Watch out for line wrap:

[BigWallop]

[geoff]

In message , IMM writes

Yes, this version - the other version is the Netaheat electronic John

If the main gas valve is opening and staying on "reliably" for a couple of minutes, then I doubt it's the relay. If the relay contacts were on their way out, I would expect it to either work intermittently or just fail. It sounds to me more like the overheat stat opening and shutting down the boiler.

I don't have any experience regarding scaling up of cast iron heat exchangers, but I would think it is likely that, for some reason, the heat delivered to the heat exchanger is not being dissipated and so the boiler overheat stat is shutting the boiler down

[geoff]

In message , BigWallop writes

But wouldn't this cause the boiler to blow the flame out immediately

[Dave Ramage]

Thanks for this- I'll take a look tonight.

Dave

[Dave Ramage]

geoff, BW,

Thanks for this info....another reason to consider a replacement rather than patch it up. It also seems that the seals are asbestos according to other posts.

This could also explain that when I tested the boiler briefly with the cover off to see if the fan was working there was a fair bit of flame emitted around the bottom of the fire box when it lit.

[Smithtv]

Hi

I`ve got one of these boilers about the same age and if I remember correctly, I think I had a similar problem around 10 years ago.

The fault was due to the flue extractor fan micro-switch failing meaning that the boiler didn`t recognise that the fan was drawing out the exhaust fumes and so it switched off.

[IMM]

Yes they are.

The Neataheat was the first pilotless ignition boiler made. It was quite advanced for its time, well by British standards. It is a "very" good and reliable boiler, although the first models out had some problems which near killed off the boiler, which were soon rectified. But times move on. It is cast iron, even in the mid 1970s it was inefficient, and very inefficient by modern condensing standards. By installing a good condensing boiler you will drop your gas heating bills approx 35-40%.

Figures like that make you sit up and look. So if this is a pretty expensive job to fix (probably £100 or more) then a new condensing boiler is well worth considering. Taking into account the money saved on repair and then on gas saved, payback will be quite soon.

[IMM]

If it was my boiler, I would replace the exhaust gas differential switch and the relay. They are both getting on.

[BillR]

I've had one of these boilers for 23 years and it still going strong. AFAIK you can't run the boiler without the cover on. I too had a similar problem some years ago and it turned out to be problem with the interlock from the fan. In my case it was a flexy tube to the diaphram switch. The seals are asbestos rope but that shouldn't be problem unless you remove or dismantle the boiler.

[Ed Sirett]

IIRC the O/H stat has to be manually reset?

I agree the relay anbd gas valve are probably fine. My guess: it's a combination of dirt on the air flow proving tubes and/or poor contact on the switch itself. I'm guessing that as the flue gasses warm up the air flow proving becomes marginal and this leads to a poor contact in the diaphragm switch which makes the clicking of the relay and the pilot gas valve. The main gas valve 'click' has very substantial hysterisis ans is unlikely to "thrash".

[Ed Sirett]

Whilst I expect a saving of upto 35% on the worst case older boilers to a modern condensing boiler you would be hard pressed to get such a saving. My combustion analyser can show efficiency (or rather inefficiency due to exhaust gas losses - which is not _quite_ the same thing). I have seen over 90% on a Keston flue; less than 70% on an Ideal Concord; and over 80% of a Neatheat. Furthermore those fgures are during operation, the heat losses when the boiler flame is out but the pump is on can only make my argument stronger. =

[geoff]

In message , IMM writes

Until, that is, something goes wrong ...

[geoff]

In message , Smithtv writes

Ah, but unless the air pressure switch is working properly, the pilot and spark won't be energised, so that can't be the case here

[bob]

This sounds like the boiler going out on High Temp, usually caused by the pump failing. Remove the large silver screw in the centre of the pump and insert a screwdriver, gently, you should feel the pump rotating. A new one is £40 + fitting

[Colin Swan]

My parents have had one for probably even longer, and they are only thinking about replacing it now due to it being a little noisy. Has been pretty reliable apart from one time that a loose screw was holding a gas valve open, which caused a leak that then caused a small explosion one morning. Was a very load bang, and the casing ended up so deformed that it would not pressurise!

I also remember helping my father move it up into the loft of their new extension - that boiler is seriously heavy.

-- Colin Swan

[Dave Ramage]

Bob,

Thanks for the suggestion. Just checked this and the pump is turning OK- there was a plastic hex head screw in the centre that unscrews and pops out a bit to allow manual turning. Got a heating engineer (?) coming around this afternoon to quote so will see what happens...

Cheers, Dave.

[Dave Ramage]

Thought I'd follow this up with the final solution!

After poking around with a multimeter for a while and not finding anything obvious with the boiler stat or air pressure switch, eventually bit the bullet and got a local boiler guy in to take a look. He poked around with a multimeter for 10 minutes or so and diagnosed the problem to be the PCB. Was initially suspitious as this happens to be one of the more expensive components! (£90 or so), but was at least quick to fit. Eventualy went for a reconditioned PCB at £30 or so. Seems to have fixed the problem. £130 incl. seems small price to pay for working CH at this time of year!

Many thanks for all the help- was worth a try doing it myself!

Cheers, Dave.