Annual Vaillant boiler F.75 error - Part 2

[Milleniumaire]

For some reason my original post on this topic has been locked, so I have no choice but to start a new thread as I would like to add some feedback.

Hi Ian, I followed your advice and set the pressure to 1.5 bar on a cold system (had to let some water out through the magnaclean to do this). I then removed the filling loop hose and turned the boiler back on. After an hour the pressure was at 1.9 bar and didn't increase above this. Unfortunately, it looks like the boiler overflow is still leaking, but slower than before.

I guess disconnecting the filling loop hose was to ensure it wasn't leaking and allowing more water into the system?

For the rest of last night, the pressures looked good, however, this morning we woke up to a freezing cold house and an F.75 error! Carefully let enough water in to clear the F.75 error but without over filling, so the digital gauge was showing 1.5 bar again. When operating, the boiler pressure is now between 1.7 and 1.9 bar, but the PRV is still leaking slowly.

I suspect as a result of the minimum amount of water being in the system and the leaking PRV, I will wake to the same F.75 error in the morning.

So, I suspect the PRV may require replacing and that may solve the issue? Tried to get in touch with my heating engineer today but without success.

I've also fired off an email to Vaillant technical support regarding the size of the internal expansion vessel and the size of my system just to get some indication of whether they think this should be rectified.

 

[muggles]

Hmm you're the latest victim it seems...it's becoming an increasing problem on this site - the moderators (who are largely anonymous) are charging around deleting random posts and locking threads with absolutely no explanation for their actions, which isn't helpful to anyone as it removes the continuity of threads and nobody ever knows what it is they might have been deemed to have done wrong. Really quite irritating.

Anyway, to your issue. If you have to get it up to 1.5 bar to clear the fault that could be indicative of an issue. IIRC Vaillants should work down to 0.9 quite happily.

As I said in my first reply to you (which you seem to have ignored beyond the first sentence), I think your PRV is knackered and you need a new one. That won't cure the F75 completely but will at least halt the water loss as it appears from what you've said that it is dripping no matter what the boiler is doing.

If your expansion vessel is undersized it would certainly help to upgrade it if you can find somewhere on the system to put a larger one

Going into the diagnostics and setting d.19 to 3 can help

Beyond that you're into getting your engineer to investigate where the pressure sensor is working correctly, whether the rubber hoses inside the boiler are degrading and blocking up, and whether the filter by the pressure sensor is blocked

Hope that helps

 

[Milleniumaire]

In your experience is it possible to clean the PRV or is it more likely to need replacing? There doesn't seem to be much that can go wrong with one other than it being blocked open by crud, or the spring breaking.

 

[muggles]

I've never successfully cleaned one - easiest to just replace it

 

[AGAS]

In your experience is it possible to clean the PRV or is it more likely to need replacing? There doesn't seem to be much that can go wrong with one other than it being blocked open by crud, or the spring breaking.

just change it for the price and always available on the shelf

edit; and thats not in B&Q

 

[ianmcd]

it does sound like your PRV needs replacing, I have successfully cleaned some in an emergency at weekends but better to replace , what model is your vaillant ?

 

[Milleniumaire]

Hi Ian, it's an ecoTEC plus 637 system boiler. Here's a photo of the PRV. When I've looked around the web I haven't seen any that look like this, even when searching for parts for my boiler model. I'm assuming they've changed the design. I believe it is part number 178985. This is what I keep finding.

 

[Milleniumaire]

My fitter is coming round at the weekend and we are going to discuss installing an external 15 litre expansion vessel and some other bits and pieces. While I've been monitoring the boiler for the last week or so, I've found the automatic air valve on the pump has been leaking, the Salus 2 port motorised valve is leaking and the top on the magnaclean is leaking, not to mention the PRV! Don't manufacturers make anything to last these days? As I can get discount at plumb center I'm looking for good quality replacement parts, although usually I can get stuff cheaper online than even my employee discount can get me from plumb center!!

I'm still a little concerned that my fitter seems to think fitting an external EV will solve the leaking PRV issue! While the system is drained to fit the external EV, I'm wondering if it's worthwhile replacing the PRV, the temperature sensor, the automatic air vent and the motorised valve. Sure, it will cost me a chunk of money, but hopefully I can forget about these parts for another 5 years!

 

[Steelmasons]

Integral vessel has a 10 litre capacity.
I usually install a 35litre external vessel.

 

[Milleniumaire]

35 litres! Wow, that's big! I'm not sure I have the space for something that big. I'm guessing there's no harm in going larger than is required?

I did originally discuss 20 litres with the fitter as I thought that would give twice the capacity as the internal so that I could simply forget about it. Given the internal is 10 litres for a 100 litre system, I believe my system is nearer 200 litres, so 20 litres I thought would be better. I'm wondering if my fitter is assuming the external EV will be used along with the internal EV, giving 30 litres! Trouble is I've then got two of the damn things that can go wrong

 

[Steelmasons]

Vessels are sized in accordance with Pre-charge pressure/working pressure/max temperature...