Vaillant Heat Only Boiler - Water Flow Problem?

[tom_plumb]

I have a Vaillant EcoTEC Plus 415 Heat Only Open Vent Boiler throwing up a F.22 fault code as soon as it ignites and then goes idle. It then sits with pump running and an S.98 status until the boiler is switched off and reset.

F.22 = Too little water in the appliance, water pressure sensor defective, cable to pump or water sensor defective, pump blocked or defective, pump output too low.
S.98 = Flow-/Return-sensor check is running, demand (DHW or heating) is blocked.

This happened after MagnaClean was cleaned, fired back up and heard a few knocks at boiler followed by it shutting down. Found fair amount of sludge at pump, motorised valve and section of pipe near F&E supply so all replaced. Thermistors also replaced. Pump sounds like it is happily sending water round system but boiler fault code unchanged.

I'm thinking sludge has been thrown into boiler and clogged up heat exchange? Or possibly PCB fault throwing incorrect error? Any agreement or anything else I should try?

 

[ShaunCorbs]

Are you gas safe registered??

 

[tom_plumb]

All work on the appliance is being done by a gas safe registered individual (not me). I am merely looking for expert third party advice from you guys on this problem.

 

[Ted808]

I had that recently!! Was scratching my head for ages- had lots of air in the boiler/system. Changed the pump and it was ok- now I have a different problem, radiators are very noisy when heating up- cust complaining? Should I have changed the system to sealed ch? I don't know! sorry to hi-jack your post

 

[Last Plumber]

Tom Plumb
Are you sure it is a 4 series?

 

[tom_plumb]

Yep, ecotec plus 415 Open Vent. Had a bit of air in the system but nothing serious.

 

[Last Plumber]

Have you done something to it like changed the PCB?

 

[Ted808]

I think it's slow flow, there's not a great enough temperature difference between the thermisters. Speed up the pump and see if that works. And is the bypass set correctly?

 

[tom_plumb]

I've managed to get a PCB which is going to be tried later but hopes are low on this. Tried pump on high setting with no luck. There is an auto bypass valve fitted but never touched the settings, shall I fully open it then?

 

[tom_plumb]

New PCB reports same fault so not that!

 

[Chalked]

Hi
It’s just lack of flow. Could be a few things.
Blocked heat exchanger.
Sludged up pipework.
Air locked.
Or pump sited too far from the boiler.

 

[Last Plumber]

New PCB reports same fault so not that!

I was thinking wrong board to be honest because I've never seen a 4 series with an F22 fault. There is no pressure sensor on them.

If a 6 or 8 series came up with F22, the pump would not run!!

All sounds strange to me. I would say @Chalked was on the right track though.

 

[tom_plumb]

Thanks guys - some good advice! Think I'll go with isolating the boiler and attempting to flush the HE as the next thing to do.