Vaillant 837 Combi Boiler - No hot water

fivefive · 14 Nov 2014

Hi All,

Got a Vaillant 837 Combi Boiler at home, it's just over 1 year old now and has been working fine, a few days ago it started having issue where hot water becomes on and off (off mostly).

Anyway, it's now displaying the following errors when I turn on the hot water tap: -

F70 Fault: Invalid Device Specific Number
F42 Fault: Coding resistor

Any idea what they means please? And should I call Vaillant to come visit or should I get my own engineer? Do Vaillant cover free of charge?

Also, does anyone if this would affect the central heating too?

Many thanks,
fivefive

landyandy · 14 Nov 2014

You should have a 5 year guarantee with your boiler so a call to Vaillant.

Andy.

Agile · 14 Nov 2014

Preoperly installed it should have at least a three year warrantee.

But that's only valid if you bother to get it serviced as required under their conditions each year.

If not its at their discretion what they do. And it sounds as if it could be expensive to correct.

Tony

fivefive · 14 Nov 2014

Any idea what would be the cause to it please?

I've called Vaillant and they said because I haven't done a service (I had the boiler over a year), they want a £285 charge to visit/fix, but it doesn't cover certain parts.

Tony, when you said it's expensive to correct, is it because PCB might need replacing? And how much are we talking about? Just so I can get a rough idea.

Many thanks!

gazdaz36 · 15 Nov 2014

It won't be a problem with the pcb it will be due to a bad connection on the wiring loom.
From the thermal fuse on the main heat exchanger the lead connects on the harness near the right hand side of the main heat exchanger. There is also a resistor that tells the boiler what size it is. Usually it's a bad connection there but occasionally it can be where the plug connects onto the pcb and the pin has been pushed out of the plastic plug block

Bunnyman · 16 Nov 2014

That's y the service is important I'm afraid, anyway u can't remove the front on these unless ur gas safe, so u have a problem. The fixed price will cover your needs

Agile · 16 Nov 2014

fivefive said:
I've called Vaillant and they said because I haven't done a service (I had the boiler over a year), they want a £285 charge to visit/fix, but it doesn't cover certain parts.

Many thanks!

So we can better understand customer thinking, why did you not bother to get the boiler serviced?

Tony

crosseyed · 8 Jan 2017

I found this thread because I have the same F70 error, though not an F42 (which would be easy). My boiler is a post-2012 618 (not a combi) and I assumed it would be the main board which I've exchanged to no avail. I'm now guessing it's logging this fault because it's getting something on its interfaces that doesn't correspond to what you've told it it is. Much more useful would be if it logged a more specific error, such as "x doesn't correspond to DSN".

The symptoms of the fault are that the pump switches on randomly for short periods, and it may also be resetting while the burner is operating.

I have followed gazdaz's advice and checked the wiring loom and connectors carefully, but can't see anything. I guess I'll have to unplug the whole lot and stick a meter on it, but even that might not reveal a connector issue.

Agile · 8 Jan 2017

The OP did not bother to get his boiler serviced.

Did you ever get yours serviced?

Has your warranty expired?

Tony

crosseyed · 8 Jan 2017

Yep, I haven't had the unnecessary annual service so the warranty will have expired. An annual service is an expensive blunt instrument which takes no account of how much the boiler has been used.

Do you have any suggestions, other than throwing money at Vaillant?

By the way, the boiler exhibited a fault from new which required two visits from Vaillant technicians to fix.

Agile · 8 Jan 2017

Useage is not relevant at a service.

Most are about £65 to £75.

crosseyed · 8 Jan 2017

That's not what Vaillant says.

I'll see if anyone else has some advice.

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Vaillant 837 Combi Boiler - No hot water

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