BG / Netaheat / red sticker.

[T i m]

Hi All,

Just a background enquiry for the gas / heating / Corgi panel if I may.

A mate has a Potterton Netaheat Electronic wall mounted b/f gas boiler of some sort and last Sunday it stopped working. He has had a service contract with BG for many years so called them out. The guy appeared on Tuesday and diagnosed a faulty fan. He was unable to remove it (insufficient access or rounded nut or summat) so told my mate he 'needed a new boiler'.

Mate called an independent Corgi guy round to quote for a new boiler and he looked at the old one and easily remove said fan. He suggested he get BT back to fit the new fan (under the contract).

Mate calls BG back and they are concerned about (now this is third party info from a non d-i-y person remember) the seal of something, 'possibly' a small pipe that (I think he said) pokes through some part of the assembly and into a grommet in the back plate? Positive pressure sense input?

The BG guy phoned his HQ, Baxi and the consequence was he decided not to fit the fan and to disconnect the gas and stick a red sticker on the boiler instead? I *think* the issue revolves around sealing this small pipe. It has been mentioned that flexible sealants can no longer be used ..??

Now I know there are issues with (some?) Netaheat boilers (or any that use the positive pressure idea) but does anyone know what the BG guy might be concerned with especially here?

He told my mate he had been doing that game for 5 years but this was his first Netaheat!?!

Mate is keen to do what's best which could well mean a new boiler but we were keen to try to understand what is really going on here please (out of general interest).

Cheers, T i m

[geoff]

In message , T i m writes

If you really want a definitive answer on this, phone me at work and ask if you can speak to John

He is of an age to have significantly more experience than anyone here

WHich is not to do anyone down, he cut his BG teeth on these boilers and knows them inside out

01923 229224

[T i m]

Cheers fella. Is this a workdays only number?

T i m

p.s. I had claimed the controller for you if / when he disposes of the boiler. ;-)

[Unbeliever]

Not a John Frowen by any chance is it?

[YAPH]

...

If he's disconnected the appliance (as opposed to merely turning it off) then he should have classified it as "Immediately Dangerous" (ID), and that should have been because it was leaking gas, or letting fumes enter the building, or suchlike immediately dangerous situations (hence the name, natch).

If he classified it as "At Risk" then he should have merely turned off, not disconnected (e.g. cut and capped the gas pipework to) the appliance.

In either case, apart from a sticker or warning triangle or suchlike attached to the boiler itself, he should have left a form saying the reason for doing so.

[T i m]

Doh, it's late .. ;-(

Aside: I had a little result today. We have had one of those Swish Autoglide curtain timers for *years* (20, from the days when we would often be out on the motorbikes till late and the dogs were at home etc). I've noticed it running slowly of late and put it down to it's general age. Yesterday it died completely. I stripped the controller down and diagnosed a failed PSU reservoir cap and picked one up from Maplin today. It seems to have cured the fault but I fitted a 35V jobby instead of 40 (thinking they didn't do a 40+V one small enough, a second look suggests they do). Anyway, I measured the off-load voltage and it was around 37, how close are the 'working voltage' values on these things would you say (I'm gonna change it anyway but ... )?

Just as well I fixed it, £230 for a new one so it would have been put back to strings!

[T i m]

Hmm. Well it was doing none of those things before or after his first visit because he couldn't manage to get the offending part out. Second visit when he chose not to fit the new fan it still wasn't doing anything bad as I don't think it would even try to fire up without the case on? Had he fitted the new fan I (we) see no reason why it would have been any more dangerous than it was before it stopped working?

Oh, well I believe he did disconnect / cap etc.

Oh ok, I'll ask my mate if he did.

Thanks, T i m

[meow2222]

If it works, it works. The harder you push those caps, the less well they last. I think the most tolerant cap I once found was a 16v lytic that had been fitted backwards on a 23v line, and was still working flawlessly after more than 20 years.

If you need to replace it one day, its better to use a cap rated to a fair bit above the voltage in use, so a 63v job.

NT

[T i m]

Yup. ;-)

That was my concern and why I was happy to take the best Maplin had to offer (or so I thought at the time) as a test to see if the unit was working at all.

Amazing! I thought if you reverse polarised lytics even by a couple of volts it destroyed some of the dielectric material making the cap vulnerable to shorting?

I actually bought a 63V one as well with that in mind but in this case it's a fair bit bigger and wouldn't go in the unit (even if I 'remoted' the cap on longer leads).

The original cap was 2200uF @ 40V [1] and 16mm diameter and 30mm long.

I note they do a High Temp range and the 2200uF @ 50V is just about as big (18mm diameter and 35mm long) and I now know that will go 'as is' so I'll get one and swap it out soon. For the time being I'm leaving the unit unplugged and just plugging it in as needed (I don't really want the cap blowing it's brains out inside this unit just when I've fixed it!).

Cheers, T i m

[1] At a measured 37V still a bit 'close' with a 40V cap but obviously ok to have lasted ~20 years!

[Jon Fairbairn]

In my experience they often explode. Not usually violently, just swell up and push the can off. Spludge. Though there was one time when someone reverse- (or over- I'm not sure I remember correctly) voltaged an electrolytic on the other side of the room and the can pinged off the wall just clear of my head. Also one of my dad's favourite TV product recall stories was of a model with an underrated/badly designed electrolytic that tended to blow the can off violently. It was mounted just underneath the neck of the tube, so sometimes ... whump!

[Andrew Gabriel]

Depends on construction. They effectively also have a reverse voltage rating, which is usually much less than the forward voltage rating (and will be a different capacitance too). The voltage ratings themselves are not absolute in any case -- the life of the capacitor and number of early failures depends on lots of things, one of which is the voltage it's charged to, but temperature and current profile are also key factors.

[T i m]

I know . When a lad I bought a bag of electrolytic's that all turned out to be very low voltage rating. Rather than just throwing them away I hooked them up to a variable PSU over a long pair of leads. ;-)

In my time I've seen a few bases left on the PCB and the mess they leave behind. Not something I've seen so much of late but now I believe the tops are designed to split open.

Nice!

Ah. ;-(

I have worked with an old TV repair man and seen a cap go off while he had his face in a set and he was left in a cloud of smoke and some party streamers over his shoulder. ;-)

Cheers, T i m

[Richard Savage]

FWIW:

As I used to understand it :-) it was prudent to choose an electrolytic with a working voltage of at least twice the operating voltage. I was shown an PSU case with a sizeable bulge in one panel caused by a big smoothing electrolytic dismantling itself.

Richard

[geoff]

yes

[geoff]

No - a "Red label" .... Johnny Walker

[Steve Walker]

I had one explode in a dishwasher some years ago, turned from a 2" diameter, 4" cylinder into a 2" x 24" spiral wound cylinder. Made a hell of a noise too!

SteveW

[Fred Carnot]

Mine did that too. I found a 'pretty close' replacement in the 'parts bin' (posh word for several cardboard boxes full of bits awaiting the arrival of appropriately shaped tuits...)

You might find this worth bookmarking in case you need something specific:

[Ed Sirett]

This is exactly the sort of situation which gets BG a poor reputation. It is true that Netaheats, Netaheat Electronics and Profiles are abut the only boilers which operate under _+ve pressure. I.e air is blown into the boiler rather than flue gases being sucked out.

Because of this the casing seals are a more critical safety component than they would be on other boilers. There are also some seals/grommets where pipes and wires enter the chamber.

By the book these have to be in good order. The circumstances do seem to leave me wondering if they are being used as an excuse. It would be a very brave, forthright and possibly foolish fitter who turns over a colleague's judgement, even when you strongly suspect that they are being over zealous for commercial gain. So now you need a repair or replacement.

[T i m]

;-)

I went to look for such myself but thought they would be as old as the ones in there!

know they are there in case etc).

Did you do anything else when you were working on the system Fred? I wasn't sure if it was worth looking at the motor or track etc?

Cheers, T i m

[T i m]

Understood, however and if I understand it correctly this 'seal' is simply the interference fit between the vacuum tube and the inner casing. If it was to 'leak' no leaks could occur to the outside of the cabinet and if it was to leak so badly the boiler wouldn't light?

Mate spoke to me this morning and said (metal) pipe goes *through* the back panel via a plain hole and then into a rubber grommet an inch or so behind. He said he can still feel the pipe as it goes into the grommet and it's held back by a clip further down (so no chance of falling out etc)?

Cheers, T i m