Viessmann 200 WB2B weather comp not firing.

DaveEFI

Heating failed after being on all day. Quick look showed water leaking from boiler. Went to bed. Next day found it to be from the hose at the top of the boiler where it goes onto the brass adaptor. Drained down the system and ordered up a new hose. Fitted the new hose and went through the filling and venting procedure. I installed the boiler myself, so was familiar with this. Pump and diverter valve both working as expected. But it won't fire. Pumps runs and just the green LED showing. Reset causes the fan to vent things as normal, but doesn't fire. The sensors (room, boiler, outside) all read ambient as expected. Temperature limiter reads 0.5 ohm approx. Flue gas sensor about 7000. No fault codes stored. No click of the gas valve etc opening, though. The leaking water did hit the spark module and the gas valve, but both had quite some time to dry out before power was applied. It didn't go near the PCB.

JharrisSeattle

Try and purge hx once more. You may have an air pocket causing the internal flow switch to not prove. This will not give a fault code and the boiler will remain in standby. If you can confirm flow across the hx you may have a board issue and will most likely have to contact techinfo line monday. If the ignitor,refractory, or inoization rod got wet it would usually display a combustion controller fault. Good luck!

DaveEFI

Thanks. Is there a way of testing the hx flow sensor or whatever? I went through the venting procedure again with no luck.

JharrisSeattle

Only way would be to choke a ball valve on the supply or return side of the boiler and listen for flow resistance through the ball valve. For testing purposes If you have a ball valve on the supply side of the boiler you can isolate it and hook a hose up to the boiler purge drain on that side. Make sure your fill system is on. If you dont get the unit to fire when you open this drain you have another issue (assuming the flow switch inside is not stuck)

JharrisSeattle

I would try this with the gas supply turned off and listen for an attempt for ignition.

DaveEFI

There's no sound of it sparking. Wish I had a schematic of the PCB - I'm an electronics type. What I haven't checked for is 240v at the input to the ignitor. But dunno when this should be present.

DaveEFI

Checked for 240v at the input to the igniter. Nothing - even after a reset. So I'd guess the system isn't being told to fire up.

GW

Jump the flow and see what happens I would do a triple back flip if these boilers had a flow issue fault code.

DaveEFI

Could you explain how to jump the flow, please? There is a flow switch shown for early boilers, but mine doesn't have one. Sorry if it's a stupid question.

CMadatMe

Actually suggest you call someone who knows how to service the boiler. All WB2B models have a flow switch.

aircooled81

Do you have a low water cut out, aux to the boiler?
I am slightly waery here, as chris has a valid point.
But since you have a volt meter, i imagine you are comfortable.
Flow switch exsists, number 33 on attached drawing. When you put your meter on volts, and across both sides of the switch, you should have no difference. If one side has voltage, and the other doesnt, well frankly its open.

DaveEFI

I have all the original documentation supplied with the boiler - I installed it myself. The exploded view given here is very different to the one I have, and my actual boiler. The hose which failed on mine and started all this isn't shown. It shows a solid copper pipe (019) here. My version of this 200 WB2B is known as a system boiler in the UK. In the diagram shown here, the flow switch is given an 016 reference. Which I assume is the 33 given elsewhere.

If the flow switch is 016 as shown in your diagram and connected to X9 10&11 but called 33 there, my wiring diagram shows no connection to X9 11 and X9 10 isn't shown at all. It does show a flow switch 149 connected to X9 5&6, but for combi only.

My parts list does mention a flow switch 023 and flow limiter 024 but only fitted to earlier versions than mine.

So you'll perhaps excuse my confusion.

I'm not a boiler tech, but reasonably experienced at electronic fault finding.

If anyone is interested in the service manual I'm working to for this boiler, it can be downloaded as a PDF here.

http://viessmanndirect.co.uk/Catalogue/Spares/Vitodens/Vitodens-200-WB2B

DaveEFI

The answer might be useful to others so here it goes. There was no 240v to the ignition unit. Checks to the PCB showed a PCB mount fuse in this circuit had failed. Replaced it. Boiler now attempted to fire, but didn't and now gave an error code EE, so progress of some sort. But still no 240v to the ignition unit. That is switched via an opto-isolator - a 3FS21. Replaced that and all good. Total cost for repair about 1 gbp. My guess is the water leak shorted out the feed to the ignition unit. Since that is mains voltage, a splashproof connector would have made more sense.