Yet another Vaillant boiler with an F.75 error!

[ianmcd]

This is a DIY advice forum and you have had the correct advice time after time why do you refuse to take it, the posters with Bunny in their name are experts on your boiler and many of us carry out work on behalf of the manufacturer, get an accredited repair engineer in and take his or hers advice

 

[Milleniumaire]

When the plumber recharged the expansion vessel he drained the boiler and the analogue gauge was showing zero, but the digital pressure reading was 1.5. He couldn't explain this when I asked about the difference. I assume this is what you mean by the cold reading.

I'm not sure what the documented discharge pressure is, but the plumber mentioned that 30 bar was when water would be discharged from the system to reduce pressure and (I think) the pressure reading flashes along with the hot water temperature when the pressure gets to 30 bar.

 

[ianmcd]

When the plumber recharged the expansion vessel he drained the boiler and the analogue gauge was showing zero, but the digital pressure reading was 1.5. He couldn't explain this when I asked about the difference. I assume this is what you mean by the cold reading.

I'm not sure what the documented discharge pressure is, but the plumber mentioned that 30 bar was when water would be discharged from the system to reduce pressure and (I think) the pressure reading flashes along with the hot water temperature when the pressure gets to 30 bar.

Well if your boiler gets to 30 Bar as you suggest then you will be able to confirm whether the moon landings were fake or not

 

[iansoady]

Hi there,

My first post...

This thread has been very useful to me.

I've been struggling with an intermittent F.75 on a Vaillant - it started about 6 months ago, around 5 years after fitting (this was an entirely new heating system). Each time the analogue pressure gauge was below the "normal" sector and was easy to temporarily sort out by letting a small amount of water in.

After some thought I decided to have a look at the Magnaclean (which is fitted in an inaccessible cupboard) - and the top was not even finger tight. It had some encrustation around it so it was clear that a small amount of water had been leaking from it. I'm sure this was the cause of loss of pressure. I had previously put a catch tank under the PRV discharge and no water came out.

After cleaning the filter (only a small amount of metallic deposit) I've refitted it and tightened the top down firmly - so hope that's it sorted.

In the hope this may help someone else......

 

[Bunnyman]

Nope that won't sort it, when was boiler serviced?

 

[iansoady]

A couple of years ago but I'm arranging a service for the next few weeks.

I would have thought that loss of water via the magnaclean would have had the same effect as a leak elsewhere in the system in that it would lose pressure?

 

[Agile]

Yes, but any leak will cause a loss of pressure.

But the F75 fault has other causes!

Tony

 

[iansoady]

Thanks for that.

According to the manual, two of the reasons for F75 (no pressure rise on turning on the pump) are too little water in appliance or air in the heating system. I was hoping that the leaking magnaclean may have been causing this.

When I get the service organised hopefully this will give a definitive answer.

 

[Hotspud999]

Hey Agile are you still about?
Having read the correspondence regarding code f75. Would the sensor still stop the boiler functioning at 3.5 bar?
And if I release the pressure to 1.0 would that cure things?

 

[muggles]

No, it's a low-pressure cut out only. If you're reading 3.5 bar and it's cut out on F75 your sensor is reading incorrectly

 

[Agile]

Or it could be at 3.5 bar and the other causes are giving the F75.

For a pro they are usually pretty easy to sort out.

But because of the design of the boiler they are not suitable for DIY repairs as a DIYer should not remove the cover.

Tony

 

[Hotspud999]

Also noticed there is a small brown pool of water next to pump! Am I up the Creek cost wise?

 

[AGAS]

try these mysticfaultfinding.com , they are excellent at getting the right price for you . you might need a little spelling variation to get it to work because i can't remember the name properly, but its like they know what exactly is going on

 

[Agile]

Or do you mean www.mysticmamma.com ?

 

[ianmcd]

Hotspud you have piggy backed onto a post that is over 2 and a half years old , if you want advice start your own post and you will get what you need