Valiant Ecotech Plus 637 - Error F76

[steveoelliott]

Hi,

 

Last night my Valiant Ecotech Plus 637 displayed Error F76. I power cycled the boiler and it has been fine for the last 24 hours having both heated water in the cylinder and the radiators in the house. A quick Google suggests this points to the heat exchange overheating.

 

I spoke to my plumber who suggested to monitor it for now and the fact that the boiler recovered and hadn't blown the thermal fuse indicates it may be a transient issue. Personally I'm not convinced having lived here for over 2 years and it's the first time we've encountered it.

 

Boiler is due for annual service next month so will have it checked properly then.

 

Would welcome any comments / experience / feedback.

Edited March 30, 2022 by steveoelliott

[Temp]

Google found..

https://pricethisplease.co.uk/vaillant-76-error/#:~:text=The F76 error code means,by a high temperature reading.

 

Has a bunch of suggestions for potential causes.

 

Perhaps start by bleding any air in the system and reseting the pressure? You might also consider getting the system drained and refilled with corrosion inhibitor like Fernox F1 if it hasnt been done in years. 

[steveoelliott]

18 minutes ago, Temp said:

Google found..

https://pricethisplease.co.uk/vaillant-76-error/#:~:text=The F76 error code means,by a high temperature reading.

 

Has a bunch of suggestions for potential causes.

 

Perhaps start by bleding any air in the system and reseting the pressure? You might also consider getting the system drained and refilled with corrosion inhibitor like Fernox F1 if it hasnt been done in years. 

 

Thanks... I had a couple of bottles of inhibitor added when system was drained to install a fancy radiator back in October. I'll take a look at the artcie.

[steveoelliott]

Today ~9 days after the first event, the boiler once again shutdown with error F.76.

 

Clearly this isn’t the thermal fuse and I be suspect if it is wiring given the fact that reset clears this condition. I have come up with a  potential trigger however… Whilst the central heating side of the boiler has been untouched; I have on both occasions turned the water off for a period and drained some hot water. Once was as we were away for several days (I did turn off the H/W heating whilst away). On our return we hit this error 4 days later. Yesterday, the water was turned off and some H/W drained to replace a shower.

 

We have a megaflow cylinder but not sure if that's relevant here.

 

Edited April 7, 2022 by steveoelliott

[steveoelliott]

Interestingly, the boiler has been stable since I lowered the radiator water temp to 55 degrees. Clearly there is an underlying issue that still needs investigating. My plumber is supposed to be checking later this week,

[Nickfromwales]

Could be the pump starting to fail, but not just stopping all together. Have you checked the automatic air vent is not blocked also, and that air is not getting trapped in the main HeatEx?

[steveoelliott]

13 hours ago, Nickfromwales said:

Could be the pump starting to fail, but not just stopping all together. Have you checked the automatic air vent is not blocked also, and that air is not getting trapped in the main HeatEx?

Thanks... I'll mention it to the plumber to check. Presumably air getting trapped in the exchanger is a byproduct of a inoperative air vent? It is interesting that lowering the temperature seems to have offered a workaround for now. The boiler is 13 years old BTW and has probably worked quite hard with 21 radiators on the system together with a megaflow.

Edited April 26, 2022 by steveoelliott

[Nickfromwales]

16 minutes ago, steveoelliott said:

Presumably air getting trapped in the exchanger is a byproduct of a inoperative air vent?

That, and also the pump not operating at full potential as the rotor is not fully immersed. That can also cause overheating ( kettling ) by water then spending too much time in the HeatEx.

I would consider changing the overheat stat also, as it runs quite close to the normal max operational temp of the boiler. You should be able to get the as-new resistance reading from the manufacturer to allow you to compare what you have, eg before removal.  

A decent plumber is always a help when trouble finding. Found 2 young guns about to remove a perfectly good WB boiler in a pensioners flat as they failed to diagnose a £6 flow switch part had failed...... They had quoted £800 labour plus the new boiler costs. Jeez!

[steveoelliott]

11 hours ago, Nickfromwales said:

That, and also the pump not operating at full potential as the rotor is not fully immersed. That can also cause overheating ( kettling ) by water then spending too much time in the HeatEx.

I would consider changing the overheat stat also, as it runs quite close to the normal max operational temp of the boiler. You should be able to get the as-new resistance reading from the manufacturer to allow you to compare what you have, eg before removal.  

A decent plumber is always a help when trouble finding. Found 2 young guns about to remove a perfectly good WB boiler in a pensioners flat as they failed to diagnose a £6 flow switch part had failed...... They had quoted £800 labour plus the new boiler costs. Jeez!

Thanks Nick. Is there a separate overheat stat to the fuse in the exchanger? My understanding from Valiant is that once the fuse goes that’s it the boiler stopped working. 
 

My research before coming here suggested a PCB issue or wiring issue to the fuse but I am doubtful of those given how it is stable with lower temp.

 

How would one deduce the pump was not working at full potential? It isn't making unusual noise and all 21 radiators get warm (albeit less warm with lower temp) but were piping hot before.

 

Valiant do have a deal where you sign up for £50 a month for 6 months minimum and they will repair the boiler as part of that unless uneconomical. If it is you can break the contract and get all money back OR get 750 off new boiler. 
 

The challenge I find is most plumbers swap parts rather than troubleshoot.

 

 

Edited April 26, 2022 by steveoelliott

[markocosic]

HX with air in it leading to higher flue temps.

 

HX with crud in it leading to higher flue temps.

 

Thermal fuse breaking down internally and going "normal" (closed circuit) when cooling down again. Not uncommon with age and operating at high temperatures. Google polish forums etc where these are repaired.

 

Can you power limit the boiler? If the HX is clogged that'll drop flue gas temps at the expense of hot water reheat output and the time it takes rather than hot water final temperature. Reheating a stolen cold tank probably had the boiler firing harder for longer and triggered the fault.

 

Else if you're sure HX is clear find a scrap boiler to nick the (normally closed) sensor out of? (I don't think it's available separately)

[steveoelliott]

On 09/07/2022 at 09:59, markocosic said:

HX with air in it leading to higher flue temps.

 

HX with crud in it leading to higher flue temps.

 

Thermal fuse breaking down internally and going "normal" (closed circuit) when cooling down again. Not uncommon with age and operating at high temperatures. Google polish forums etc where these are repaired.

 

Can you power limit the boiler? If the HX is clogged that'll drop flue gas temps at the expense of hot water reheat output and the time it takes rather than hot water final temperature. Reheating a stolen cold tank probably had the boiler firing harder for longer and triggered the fault.

 

Else if you're sure HX is clear find a scrap boiler to nick the (normally closed) sensor out of? (I don't think it's available separately)

Thanks... Now it has given up completely and always showing F.76.

 

I spoke to Valiant and they do a package where you pay ~£300 for 6 months cover and as part of this they will fix the boiler unless beyond economic repair. If it is then they will either refund the money or give you £750 off a new boiler so it is a no brainer. I will be doing this before the winter but for now just using the immersion on the megaflo.

[markocosic]

Checked if it is cheaper to buy another boiler for cash rather than at full list (less £450) from Vaillant? I should think a new HX would deem it a write off.

 

The fact or took a while to finally "blow" suggests old age death of fuse rather than overheat IMO.

[steveoelliott]

8 hours ago, markocosic said:

Checked if it is cheaper to buy another boiler for cash rather than at full list (less £450) from Vaillant? I should think a new HX would deem it a write off.

 

The fact or took a while to finally "blow" suggests old age death of fuse rather than overheat IMO.

I guess Vailant would carry fuses if this was the case but the labor to get to it might be prohibitive.

 

I will check that quoted pricing isn't inflated

 

Agreed on the failure pattern.