Vaillant EcoTec F76 Fault code

[LeadFarmer]

I have just had the F76 fault code on my Vaillant EcoTec Plus 837 which was installed in 2010, which I know relates to a cut off switch detecting overheating of the heat exchanger.

My plumber suggested I contact Vaillant directly as they offered a £299 fixed price repair service. I phoned them last Friday but sadly this doesn't cover the heat exchanger, but the lady at Vaillant suggested their 6 month care policy @ £50/month for 6 months (total £300) which includes repairs to any part including the heat exchanger, or a £700 contribution towards a new boiler if uneconomical to repair.

I signed up there and then and they had an appointment slot for following morning (yesterday) at 8:30am which I booked. The guy arrived and swapped the control panel, G10 seal and gave the boiler a clean. The boiler worked fine for 24hrs and then this morning the F76 fault code reappeared, with the boiler shutting down.

Seeing as its now Sunday Im calling them back tomorrow and I guess they will now replace the heat exchanger, or give me £700 towards a new boiler. I assume the contract ties me to buying a new boiler from them, and having them fit it?

 

[Gasguru]

F76 is a rare fault code...the boiler should shut down with the temperature sensing fault codes before the heat exchanger flue gas sensor finally gives the F76. Quite often the fault code is due to poor contacts on the connector near the sensor....was this a genuine Vaillant engineer that turned up? AFAIR the sensor is only available to Vaillant engineers...it's a thermal fuse and once tripped it's scrap. To us non Vaillant the only choice is a new hex. I don't get why he would replace the pcb.

 

[LeadFarmer]

Yes it was a Vaillant guy, despatched by Vaillant and arrived in a Valiant van.

The F76 fault code first appeared a few weeks ago, but turning the boiler off/on cleared it for a day or two, but it kept reappearing. My usual plumber cleaned all the connections which solved things for a few days, but the F76 code reappeared, which is when I phoned Vaillant.

 

[Gasguru]

AFAIK once you get an F76 it's permanent as the sensor fails on overheat so the boiler shouldn't reset. I wonder if that's why the pcb was replaced. Iffy wiring maybe?

 

[LeadFarmer]

Sometimes turning it on/off clears the fault code, but I realise thats not safe because if it is actually overheating then it shouldn't be used.

But now the hot water is working, but no central heating.

Something certainly isn't right.

 

[Gasguru]

The Vaillant techs reckon it's 90/95% chance the F76 is due to dodgy wiring/connectors. If the thermal fuse has genuinely failed you should not be able to reset the boiler...it would always come up with F76. You would normally get other temperature or circulation fault codes before a genuine F76.

 

[LeadFarmer]

Im sure you are right, otherwise I wouldn't be able to reset the boiler by turning on/off.

But if its still doing it even with a new PCB, then Ive no idea here the sting fault could be. I guess time will tell.

 

[LeadFarmer]

Having had the F76 fault code reappear over the weekend, I phoned Vaillant this morning and they are sending another engineer round again tomorrow. At least thats good service.

 

[ScottishGasMan]

If the thermal fuse has gone because of a genuine overheat of the flue gas (which normally would need a load of things to fail first) then it is not reseatable. The fuse its self is not even available to vaillant engineers, for the reason being that if it has been tripped then the heat exchanger will already be damaged (although not likley visibly damaged)

Some guys will have spare fuses taken from heat exchangers that have been noisey or leaking, so they can get it up and running again if its the case that its just been a bad fuse.

The likley hood is either the wiring harness will have a poor connection or more likley (given the age of the unit as wiring issues like that normally come from the factory with poorly pressed wring connectors) the fuse is dodgey and would probably need the heat exchanger replacing.

 

[LeadFarmer]

2nd Vaillant engineer called today and replaced the wiring loom leading to the thermal fuse as he said there looked to be a bad connection. He said the thermal fuse had tested ok.

 

[LeadFarmer]

And an hour after he left the F76 fault code has returned!!!

Ive phoned Valiant and they have phoned their engineer who says he's ordering a part and they will be in touch soon to make another appointment to visit again. I can only assume they might finally be replacing the heat exchanger, though both engineers have told me my heat exchanger is fine. Maybe it needs replacing just to get the new thermal switch?

So up to now for my £300 6 month care plan I've had a new control panel, new wiring loom, new G10 heat exchanger seal and some adjustment to the flue, and may yet be getting the heat exchanger replaced? Oh, and 6 months cover remaining on my Care plan. Im glad I didn't choose their £300 fixed price one of repair as they might have tried to wriggle out of returning?

Not bad value I guess, but I just want heating and hot water!

 

[Gasguru]

If the idiots had used a thermistor (as most manufacturers chose to on that hex) rather than a thermal fuse the software could monitor the temperature to see if it's a genuine issue.
Sounds like an iffy thermal fuse...and they'll need to replace the whole hex.

 

[LeadFarmer]

They are returning tomorrow to fit a new heat exchanger.
Im guessing they try the cheapest methods of repair first, seeing as the heat exchanger is probably the most expensive part?
All I need now is a new diverter valve and expansion tank and ill pretty much have a brand new boiler!!!

 

[Gasguru]

Cost to Vaillant no more than £50...cheap really.

 

[hertsboilers]

F76 is a rare fault code...the boiler should shut down with the temperature sensing fault codes before the heat exchanger flue gas sensor finally gives the F76. Quite often the fault code is due to poor contacts on the connector near the sensor....was this a genuine Vaillant engineer that turned up? AFAIR the sensor is only available to Vaillant engineers...it's a thermal fuse and once tripped it's scrap. To us non Vaillant the only choice is a new hex. I don't get why he would replace the pcb.

I referred one for Vaillant fixed price repair early this week, the customer was told the same thing as OP, it is a contract with Domestics and General. It seems better than Vaillant own package, so the customer went to 6 month contract by £50. The local Vaillant engineer turned up on the second day, not from Domestics and General.