Yet another Vaillant boiler with an F.75 error!

[Milleniumaire]

I have a Vaillant ecoTEC plus 637 system boiler, which was installed just under 3 years ago (April 2010). Of course, it's out of warranty now that the problems have started! The boiler was only serviced 3 months ago by the original installer.

Last Tuesday we woke to a cold house caused by the boiler not working. The analogue pressure gauge was at zero and F.75 was showing in the display.

I opened the filling loop and let more water in. Turned the boiler off and back on and all was okay.

On Friday morning same again. Cold house, no pressure on analogue gauge and showing F.75. Refilled and working okay. At this point I decided there must be a leak, causing the pressure to drop, although I'm not sure why this would be reflected by a F.75 error, rather than an F.22! I spent half an hour checking all the pipes around the boiler and all the radiators in the house, but found no sign of leakage. I guess it's possible that pipes under the floor boards could be leaking, but couldn't see any sign of damp patches on any ceiling, so the only place left to check would be under the downstairs floorboards, which I can't get under (due to tiles etc.).

It seems strange that this issue is happening during the night, possibly because the backstop temperature is set to 15, so the boiler stays off most of the night, allowing the system to get cold (and allows the pipes to contract?).

I turned the temperature down to 15 on Saturday during the day and left it for a few hours, in the hope of seeing a leak or a repeat of the problem, but it didn't happen and once the temperature was turned up the boiler fired up and worked as normal.

Each time I've allowed more water into the system I've noticed water coming out of the external overflow pipe, but I suspect this is because I've put too much in and it is simply allowing water to escape to reduce the pressure. Currently, the analogue pressure gauge needle is towards the top end of the grey and the digital reading is showing 2.8 bar.

As this has happened twice in a week, I've no reason to suspect it won't happen again, but currently it seems to be behaving.

Am I worrying unduly or am I experiencing the start of the dreaded F.75 problem?

 

[twgas]

You need to recharge the expasion vessel, once that is done the discharge pipe will need checking to see if its staying dry or not.

 

[Milleniumaire]

Thanks Mick.

The system has an external expansion vessel and I believe there is also a small expansion vessel fitted inside the boiler, so this complicates things.

As I also don't know what the pressure should be I've decided to try to get the installer back, unfortunately he's always very difficult to contact (I guess he's a busy bloke).

Out of interest and so I can understand things a little more, why does the F.75 code display, rather than a code indicating there is a lack of pressure (such as F.22)?

Also, why is it that when I allow more water into the system, to increase the pressure, it loses pressure again? Where is all this extra water going?

Thanks.

 

[Agile]

It sounds like the pressure in the external EXV is wrong and its not doing the job.

A DIYer should not be opening the boiler to access the smaller EXV inside because the front cover is the combustion chamber seal.

The failing EXV will be creating the F75 error and expelling water from the PRV vent.

There is a special procedure for repressurising EXVs ( see FAQ ) and I am sorry to say many engineers dont know it even some British Gas engineers.

If you run the system at 1.5 bar then the EXV should be pressurised to about 0.9 Bar ( or about 10 psi ).

With the system cold run the heating starting from a pressure of 1.5 Bar and see what it gets up to when the rads are all hot.

Tony

 

[Milleniumaire]

I did what you suggested and turned the boiler off for a couple of hours, so the radiators were cold. The pressure was showing 1.8 bar.

When turned back on, after an hour the pressure was up to 2.8 bar and the radiators were almost too hot to touch.

No problems with error codes and everything working as expected.

 

[ianmcd]

Your system pressure should not rise to 2.8 Bar you have an expansion problem somewhere, this can be caused by various things , faulty expansion vessel, wrongly sized expansion vessel, over or under pressurised expansion vessel, blocked communication hose/pipe why not just bite the bullet and call in someone that knows what they are doing

 

[Milleniumaire]

As I said in my earlier post, I intend to get the original installer back to look at the problem, but given it is the weekend, I don't expect him to return my calls until tomorrow at the earliest.

Using a qualified installer doesn't prevent my curiosity from asking questions. Hopefully I will then have a little understanding when he explains the problem, and the solution.

 

[ianmcd]

As I said in my earlier post, I intend to get the original installer back to look at the problem, but given it is the weekend, I don't expect him to return my calls until tomorrow at the earliest.

Using a qualified installer doesn't prevent my curiosity from asking questions. Hopefully I will then have a little understanding when he explains the problem, and the solution.

Of course and that is the correct thing to do, but to say "another Valliant F75 code" is not fair, you have a very decent boiler but it can not control what your system water does and the boiler is only protecting itself and the rest of your system by cutting out when the pressure is too low every modern boiler will do exactly the same so not fair to make out that it is the boiler manufacturers fault and no before you ask I do not work for Valliant

 

[Agile]

As I said in my earlier post, I intend to get the original installer back to look at the problem, but given it is the weekend, I don't expect him to return my calls until tomorrow at the earliest.

I have some concerns about his ability to set up the EXVs correctly!

Not answering calls at the weekend adds to my concerns. I always answer my phone or call back asap.

I asked you to set the cold pressure to 1.5 ( not 1.8 ) and see what it went up to.

1.8 is too high and we now know that the EXVs are not working correctly.

Tony

 

[Milleniumaire]

but to say "another Valliant F75 code" is not fair

Have you Googled "Vaillant F75"? There are a raft of issues relating to this code, which appears to be a catch all, some of which are known by Vaillant, but they refuse to accept there is a problem. I even found reference to a "Vaillant F.75 repair kit". This is why I used the title "Yet another Vaillant boiler with an F.75 error!".

Based on the guidance I've received from this thread so far, I may be lucky and the issue has nothing to do with the boiler, so maybe I was being negative with my title, but it gave me that "oh no, not again" feeling as I had 5 years of pressure issues with my previous boiler and that was the reason for changing to the Vaillant.

I have some concerns about his ability to set up the EXVs correctly!

The system has been working okay for the 2.75 years upto now. Maybe I've been lucky! One thing that has changed in the last month is that I increased the heating curve as the house wasn't warming up enough. I assume this would have an effect on pressure as the CH water will be hotter, but I would have expected the system to handle this.

Not answering calls at the weekend adds to my concerns. I always answer my phone or call back asap.

It always takes me a few calls, voicemails and texts to get his attention. He's always very apologetic and explains that he's very busy. I'ts not too much of an issue with my current problem - it's not like I don't have heating or hot water, but I confess I might get annoyed if it was an emergency, but then I would try much harder to contact him!
As it isn't an emergency I'm not surprised that he would wait until a week day to return my calls.

I checked the pressure before leaving for work this morning and it was showing 3.2 bar. I could see signs of water from the outside overflow pipe, so I guess this explains where all the extra water is going that I have to add to the system when the pressure reduces. Clearly this is a spiral that will continue until this issue is resolved.

 

[Agile]

The system has been working okay for the 2.75 years upto now. Maybe I've been lucky! One thing that has changed in the last month is that I increased the heating curve as the house wasn't warming up enough. I assume this would have an effect on pressure as the CH water will be hotter, but I would have expected the system to handle this.

As it isn't an emergency I'm not surprised that he would wait until a week day to return my calls.

If you thought for a moment you would perhaps realise that running the system hotter increases the expansion so any problem with the EXV will be exacerbated.

Running for a few years will eventually cause a problem if the EXVs have not been topped up at services. Those of us who are aware of boiler problems ensure we always top up EXVs on boilers known to be sensitive.

Many installers are just that and dont have experience of repairs to boilers.

There is no F75 design problem with Vaillants but they have sophisticated monitoring and take action to protect the boiler if any parameters are out of the set tolerances. This will happen on a dirty system or of the EXVs are incorrect.

I would always return calls to customers at weekends as sometimes I can tell them something simple to do like topping up the pressure. During the discussion we discuss when I would go. I doubt he even listens to calls at the weekends, many dont. To me it differentiates between those keen on good customer service and those who are not!

Tony Glazier

 

[Milleniumaire]

There is no F75 design problem with Vaillants

I think a lot of people might disagree with you on this point:

http://vaillant-ecotec-repairs.co.uk/Vaillant_ecoTEC_F.75_Fault_Code_help.html

http://www.ebuild.co.uk/topic/10629-any-vaillant-combi-experts-here/

http://community.screwfix.com/message/73861

//www.diynot.com/forums/viewtopic.php?t=90380&start=15

https://www.heatingspares247.com/ad...ds=20023721&osCsid=5mj2ghq8t5saknbl07dgkg84o6

Of course, this is likely to only be a problem with a small number of Vaillant boilers in the grand scheme, but the fact that there is a "repair kit" suggests it is a known issue.

Hopefully, this isn't my issue.

 

[Agile]

Boilers installed on dirty systems and those whose installers dont know how to pressurise the EXVs correctly will always cause problems.

I have never needed to fit one of those kits and have always managed to deal with any F75 errors!

Tony

 

[ianmcd]

Based on the guidance I've received from this thread so far, I may be lucky and the issue has nothing to do with the boiler, so maybe I was being negative with my title, but it gave me that "oh no, not again" feeling as I had 5 years of pressure issues with my previous boiler and that was the reason for changing to the Vaillant.

Read more: //www.diynot.com/forums/plumbi...oiler-with-an-f75-error.357112/#ixzz2MbXMgzfZ


So would that not suggest to you that the pressure problem is with your system and not your new boiler ???? you can fit any boiler you like but it will not sort any pressure problems you have outside the boiler

 

[Milleniumaire]

I realised today that the external expansion vessel is for the UniSTOR unvented cylinder, which sits next to the boiler. This EXV is therefore for the hot water supply and is nothing to do with the CH side of things.

This suggests that if there is a problem with the expansion vessel, it is the small one built into the boiler. Also, don't these built in vessels come pre-charged? If so, it isn't really possible to blame the installer for not correctly charging it.

I couldn't resist taking the front cover off the boiler today. It's the first time I've seen inside and I'm very impressed. Everything looks to be good quality.

I briefly pressed the valve on the expansion vessel and air, not water came out, so I think that suggests it hasn't failed.

Unfortunately, I'm still waiting for my installer to get back to me. I know he skis, so it may be that he's on holiday, or he could be ignoring me!

I've just got the number of a couple of plumbers in my area from the Vaillant website, so maybe I'll try and get in touch with them instead as I'm starting to get a little concerned about the continuous high pressure of the system.