Boiler broke ;-)

[Dave Plowman (News)]

Hose arrived and fitted. Didn't remove the old until the new one was here. Bit of a fiddle getting at the spring clip towards the back of the boiler

- jubilee ones would be easier.

But no split in the old hose I could find. So it may just have been leaking past the clip. Another reason to use jubilee. ;-)

Got it re-filled and vented. Bled all the rads. No leaks while cold, but pressurized.

But the boiler won't fire. Pump is running as is the fan. Diverter valve ok too. No sounds of sparking from the igniter.

Looked at everything the water leak could have got at and seems ok.

The Viessmann service manual isn't the easiest thing to understand. Possibly a direct translation from German by someone like Wodney. Keeps on referring you to a page number which is wrong.

It suggest checking the continuity of the 'temperture limiter' if it fails to fire. (basically, the theremocouple, but electric) That's OK.

Stored fault code is Eb. Burner in a fault state. But following the 'action' instructions for that doesn't seem to sort it. Think I'll have to get a man in.

I really, really hate these thing where you access the software settings via the built in controller. Be much nicer to plug in your laptop and be able to see what you're doing.

[Thomas Prufer]

Ask geoff first, there may be a magic incantation to reset, or a common fault...

Thomas Prufer

[Dave Plowman (News)]

Sadly, it's not a mainstream boiler.

[Stuart Noble]

Hate to say it but sounds like maybe the hose wasn't leaking. Anything else in the vicinity?

[David]

Hmmm. I know yours is a different model, but the igniter module failed on my similarly-aged WB1A just outside warranty.

I'd heard they were suspect, so I already had a replacement at the ready. What I hadn't bargained for was the defective module also taking out the relevant bit of the PCB when it failed :(

So I had to pay for a fixed-price Viessmann repair, to have a new PCB fitted. Disappointing. I hope you haven't suffered a similar fate.

[John Rumm]

Is there an inline filter after the rubber hose?

There was a design flaw on the older Vaillant ones that used rubber hoses to connect bits of the system internally - they seemed very good at collecting any scale or sludge on the inside of the hose. This was ok until someone squeezed one, and the broke lose, then made its way to a (very small) inline filter and clogged it. Perhaps yours is similar?

(newer versions, and retrofit parts now feature a carefully folded up and telescopic section of copper piping to replace the rubber)

[Dave Plowman (News)]

Luckily, the leak was in an easy place to inspect. The hose went on to a brass elbow attached to the heat exchanger. No sign of it leaking other than between the hose and elbow.

It continued to leak even with the boiler switched off and the pressure at zero. The new one isn't leaking, with the system pressurized. Of course the real test will be with it up to temperature.

[Dave Plowman (News)]

Right. Did it throw up an error code?

Oh dear.

It's odd there would be two faults at the same time? The leak was so bad it couldn't have been like that for long. Water did get on the igniter module, though. But not much, and it's a sealed unit.

[Dave Plowman (News)]

Not shown in the manual exploded view or mentioned in the text.

Water appeared to be circulating ok by the gurgling noises on filling,and the air from the bottle when doing the venting procedure. With the pump running now, it all sounds quiet, and I can feel the water pulsing through the rads.

[Stuart Noble]

This fixed price repair lark, coupled with ridiculous spare part prices, is making it difficult for engineers or d-i-yers to fix anything in a boiler and make a profit. I had the heat exchanger and a couple of other components replaced by WB for £300. My local guy said the parts alone would be £250+ and, given that the WB engineer spent 2 hours getting the old one out, one can see the sense of fixed price repairs if you have a good idea what's at fault.

[Bob Eager]

A couple of years ago, our WB failed. I called them out on the £300 fixed price (included cover for a year, otherwise it would have been £260).

It was a leaking 'something' that let the wiring harness get too hot and it melted. New harness and a load of other stuff. 3.5 hours work for a near complete rebuild.

[Stuart Noble]

I know I've spouted this before but, if someone has to take time off work for the various ins and outs of a local plumber, this option could be a no brainer

[David]

on my similarly-aged WB1A just outside warranty.

I don't remember - sorry.

Yes, I agree it's odd. Could it be related to the boiler not having been u sed for a few days, I wonder?

Another problem I had with my WB1A was, on returning from holiday, the boil er wouldn't light. That was due to a sticking mixture damper valve (a.k.a. "flapper valve" or some such) which is apparently another well-known fault . That did produce an F4 (AFAICR) code. It's sandwiched between the fan a nd the combustion chamber, and required a poke to unstick it. Later iterat ions of said flap are supposed to be better in this respect. Indeed, I bel ieve the previously-mentioned fixed-price repair included swapping the "fla pper" as a matter of course, and we've not had the same problem again.

Might be worth a poke?

[David]

I agree. In my case, I was confident I'd narrowed the problem down to the PCB, and I seem to remember the fixed-price repair was actually cheaper tha n the PCB price, and included a full service :)

[John Rumm]

I did once get a spurious fault code on (first) startup on a new Vaillant where one of the internal bleed nipples was ideally rotated to squirt water into a connector for a sensor when you purged it! However, once it was reset and allowed to dry out it was fine again.

[Dave Plowman (News)]

Can anyone take me through the ignition sequence of a modern boiler?

Think I understand how the older thermocouple and pilot light type worked.

How does a modern one know it is sparking before turning on the gas? Or does it simply turn on the gas and assume a spark, then turn of the gas if it's not fired within a given time?

IIRC, what this one used to do at switch on was to run the fan at full belt to clear out the combustion chamber and assure there was fresh air. There would then be a click - I assume the gas valve opening - and it would fire immediately. You could hear it burning. ;-)

It does run the fan, but no click. After a short while you can hear the diverter valve move - I assume because the hot water side is calling for heat.

Everything I look at in the service manual seems to say the red LED will be on if any form of lockout occurs, and will need a re-set. But this isn't the case here - it's out. But does come on as normal during the self test at switch on, then goes out.

[Roger Mills]

My Baxi Solo isn't exactly 'modern' (about 25 years old) but it is fan assisted, and has a start-up sequence.

First it turns the fan on. There is an air pressure switch which detects that the fan is running.

Provided the fan is running, it then turns on the gas to the pilot jet and starts sparking. It detects that the pilot jet is lit by means of some sort of flame ionisation detector. If the pilot doesn't light for some reason, it goes on sparking indefinitely. [The small amount of gas is presumably blown out of the flue by the fan]. Provided the pilot jet

*is* alight, it stops sparking and opens the main gas valve to light the burner.

My boiler has several LEDs which light in turn (cumulatively) showing how far it's got through the sequence. Under normal circumstances, they all light more or less simultaneously because the whole sequence is quite fast.

[Dave Plowman (News)]

So do all have a pilot jet? Not really sure mine has. Thing is I'm not hearing any valve open after the fan had done its initial fast bit.

[Roger Mills]

I don't have experience of a wide enough range of boilers to be able to give a definitive answer, but it's my understanding that that's how most work.

Do you have a spare parts list, showing a picture of the gas valve? If it's two valves in one - as many are - it should be obvious from the gas and electrical connections.

Does your service manual have a trouble-shooting flow chart? the one which came with my Baxi is reasonably good - tho' it did tell me that I needed a new PCB when the real problem was a bit of crud deflecting the pilot flame which stopped the flame detector from working. Fortunately, I didn't believe it.

If the fan is working but nothing else happens, maybe the pressure switch is duff. If you're brave enough, try by-passing it and see whether the boiler then fires.

[Dave Plowman (News)]

What I'd really like is a proper curcuit of the boiler electrics - even as a block schematic. All I've got is the external connections to the control unit.

It's fairly typical of such documents. Expects the average boiler service type to have no knowledge of electrics, so no point in confusing them. You can't even buy the PCB on its own. It comes complete with housing.