Boiler fault

[Dave Plowman (News]

The 200w wb2b system boiler which has given decent service has packed up. On power up, it normally does a self test - motors everything before firing up.

Now, just the fan comes on. At low speed. And after a minute or so of nothing, the fault light and code F9. Which translates to fan/burner fault.

Getting too old to play with such things, got a man in. Chosen at random from a Viessmann list on their site, and local.

Didn't see what he did - but could hear he ran off water. I assume hot tap. Which did sort of confuse me considering it's not a combi.

After about 20 minutes, announced he couldn't say for certain what the fault was. Could be the fan. or the PCB. Or anything. Went out to his van to consult someone. Came back and said £1100 to replace the fan assembly. And no guarantee it would fix things, so a gamble on my part. And recommended replacing the boiler. At £3500.

The fan assembly costs £200 new from Viessmann Direct. £60 from Ebay refurbished. It's held in place by a few easily accessible bolts and I'd guess can be removed in minutes. So £900 labour simply saying they don't want the job.

I've contacted Viessmann via their website, and hope they can supply an engineer who actually knows this boiler.

In the meantime I'm going to remove the PCB and look for any obvious signs. There are soldered in on board fuses not covered in the service manaual, and driver transistors that are easy enough to check too.

[Tim Lamb]

In message [e-mail]>, "Dave Plowman (News)" [e-mail]> writes

Look carefully at components likely to need more heat for successful soldering. Soldering baths may save labour but have downsides.

>

[SteveW]

Just general thoughts applicable to many boilers.

My first thought would be, is there a pressure switch to prove fan operation? If so, run with the covers off and try shorting the switch while the fan is running. I have had the micro-switch that is operated by a diaphragm fail and I have had the tubing that connects the diaphragm fail.

However, my next thought would be that the length of delay before the fault comes up would suggest that the fan is being proved, but the pilot for the burner may not be getting gas (a solenoid problem or PCB problem); failing to ignite (Spark gap or PCB problem); or igniting, but not being proved (a flame sensor or PCB problem).

[Brian Gaff]

Yes, I used to work near several when I used to work, and there were two types, straight baths where first flux then solder was applied, and flow baths were a kind of mini wave went along the pcb and soldered it. These were used to reduce heat stress on semiconductors of course. If its a surface mount jobby these do degrade over time as many used lead free solder which is rubbish at flowing. Brian

[Brian]

Just a suggestion, based on some details in your post and something I’ve seen before.

Some boilers ( we had one, which is where I say it) have a ‘positive pressure system’ ( my words for it). This is a sealed ‘box’, sealed from the room, which the fan increases the pressure in. If the system doesn’t detect a positive pressure, it won’t allow the boiler to fire or at least not for long.

In our case, the inner cover wasn’t sitting right after I’d replaced a part. There was a rubber seal.

I’d check if you have an inner cover. If you do, is it sealed, perhaps the rubber has perished? There was also a pressure sensor. On ours, it was obvious connected by a clear tube. You can hear you fan so that is probably working.

No guarantee this will help but have a look.

[Spike]

Just had a WB heat only boiler fitted to replace ancient non condensing Potterton.

Fitter was here for 11 hours on the Friday and 2 hours on Saturday. Price included boiler, fitting, filter, hose replacement on the towel rail, and a lovely job of boxing in the pipe work. Seven year guarantee if regularly serviced. Total cost £1670.

Only used so far for DHW and keeping the heat store topped up; efficiency savings are currently 10% but the DHW is a lot hotter. And the WB is very quiet.

[ARW]

Have you given Geoff at CET a call? He might have some known test voltage points or powering up sequences to look for.

He is alive and well - I got an email from him yesterday.

[Tim+]

Knackered bearings? They do wear out.

If the speed is too low it’ll never generate enough pressure to trigger the ignition sequence.

I’d be tempted to try an eBay replacement fan first.

Tim

[Roger Mills]

Sounds very likely. Worth trying a careful application of WD40 to the fan bearings to see whether that makes it run faster. That may be all it needs to generate enough pressure to trigger the pressure switch.

Do you have an installation manual for the boiler? If not, you can probably download one. They usually have a trouble-shooting flow chart which you can work through to narrow down the problem.

[Thomas Prufer]

Wot Adam said:

cetltd.com

geoff formerly posted here, and knows what to ask to get the answer to what's wrong. Ask him.

Thomas Prufer

[Brian]

A proper spray lubricant- perhaps PTFE based- would be better or spray grease. WD40 isn’t really a lubricant and ‘washes’ away oil / grease etc.

[Dave Plowman (News]

What I'm not sure is if it is the fan or the electronics which set the speed which have failed. Or some other part of the self test that has decided it's not going any further, so not running the fan at full pelt. The fan (at its slow speed) sounds perfectly normal.

Decided to have a look at the PCB, since that is free. Basically to check all the onboard fuses not mentioned in the service book. All OK, but found a popped 220mf 35v 105c cap. Not having any exact spares 'in stock' have ordered some in. Couldn't find a schematic of the PCB online, so not quite sure what this cap does.

As regards the fan replacement, a few offer recon ones. Both outright and exchange. Outright doesn't include the gaskets. Exchange want the old one before sending out the new. And can't seem to find the gaskets on their own at Viessmann Direct.

[Dave Plowman (News]

Yes I have. Both the installation and service manuals. But everything seems to revolve around fault codes. And the only fault code showing is F9

- fan/burner.

Hence getting in an engineer - thinking his experience would be greater than mine.

[Dave Plowman (News]

Thanks Adam, but according to his site doesn't do Viessmann. And no PCB listed for mine.

[Andrew]

Neighbour paid BG £5,500 to fit a WB Junior in an upstairs bedroom cupboard about 4 metres away from the Baxi Bermuda back boiler in the lounge below. Also fitted a new hot tank and condensate pump because there was nowhere to drain the condensate (allegedly).

I told him at the time that he should have got a local person to do it.

Now his gas has been shut off by Transco because the

3/4 inch iron pipe that runs from the garage (meter) under a metre-wide path and up inside the solid floor, th buried in the screen to behind the Baxi BB is leaking. Transco bloke advised him to avoid BG like the plague !, and get a local person to run some 22mm copper *overhead* from garage to the gable end of the house and in from there.

[John J]

Coincidentally I spoke to Geoff at CET yesterday. He has repaired a faulty Resol solar hot water controller for me. No doubt he can provide/recondition fan or PCB for you.

[Dave Plowman (News]

Just an update. Got a quote for a choice of new boilers from the chap who called on Monday, called out to fix the existing one, but apparently not capable of doing so.

The email subject was Quote's (sic). Repeated in the text.

The two quotes were Word attachments. Full pretty header graphics - but no VAT reg number. Address a private street in Mitcham.

Both quotes said the same - remove existing 200w combi boiler and replace. With either a 100w at £3960 (inc VAT, which was quoted separately) or £4560 (inc) for a 200W. Both with Magnaclean Pro-2. Which would involve moving the boiler position and therefore flue - and the brickwork would be made good with 'cement'

The email asked for confirmation it had been received.

Wonder if I should? Asking them if they would trust an installer who can't repair a fault on the same make as they are selling - when all parts are still available? And who can't tell the difference between a combi and system boiler?

[Dave Plowman (News]

Can someone describe how these variable speed fans work?

It has two wired connections. Power, 3 pin, using normal mains flex and colours. And a 3-pin data connector with only two wires to it.

I'm guessing power and tach?

I've ordered up a new fan from Viessmann Direct. £212 including postage. Should arrive tomorrow. If that doesn't fix it will have to investigate how it's driven on the PCB. Extensive Googling failed to find a schematic for it - the service manual does give the external connections, though.

I also downloaded the installation instructions for the latest 200W system boiler. At first glance, it looks to be almost a direct replacement as far as pipework and flue position. But I'd rather get this one working again for a few more years, and then decide if a heat pump makes more sense.

[Pamela]

[SteveW]

It doesn't surprise me. Back in 2002, it was £127 for a replacement fan for my boiler (B&Q were selling off stock, so the whole boiler got replaced for £150)! You couldn't just buy the fan, it came mounted in a housing, with the pressure switch, sensor tubes, power and signal leads, etc. If you could just buy the motor, it would have been a much cheaper and still easy swap.