Yet another Vaillant boiler with an F.75 error!

[Milleniumaire]

So are you saying the vessel was charged with 1.5 bar showing on the digital gauge with boiler empty?

That's right and that's why I queried it with them (father an son team of local, Vaillant registered plumbers).

They waited about 15 minutes with the gauges showing these settings, to see if the CH water cooling down would have an effect. They also allowed more water out. Neither had any affect on reducing the digital gauge which continued to show 1.5 bar.

was the pressure sensor removed and checked/cleaned/replaced?

No they didn't do any of this. I did list the 4 things that I've seen mentioned as reasons for the F.75 error:
- Pump
- Expansion Vessel
- Pressure Sensor
- Filter

They were always of the opinion that it was an expansion vessel issue.

i would say analogue gauge would be correct due to gauge showing a pressure drop/rise on emptying/refilling (tube not blocked).

That contradicts what Vaillant technical support told me, but then they didn't really answer my question anyway, which seems to be a regular occurrence when I contact them (usually by email). The stock response is usually for me to get a plumber round - so what is the Homeowners Techincal Helpline for then?

 

[gaswizzard]

I did list the 4 things that I've seen mentioned as reasons for the F.75 error:
- Pump
- Expansion Vessel
- Pressure Sensor
- Filter

Add blocked hoses to this , if I had a pound for every hose I've changed due to F.75 i'd be a rich man.

If a hose issue causing F.75 then the way to cure is to squeeze hoses while boiler is running although this will in turn send all the black ****e around the boiler/system...........

DISCLAIMER ....don't try this at home.

 

[gaswizzard]

Get a service carried out by someone who's familiar these boilers , also have a secondary vessel fitted (24/35 litre)

Things to check/change.................

Hoses
Canoe filter
Burner door seal
Combustion check
Internal vessel.
Pressure sensor.

etc etc...........

Get these things checked/replaced and you'll have a happy boiler.

 

[Milleniumaire]

Get a service carried out by someone who's familiar these boilers , also have a secondary vessel fitted (24/35 litre)

The boiler was serviced by the original installer in November last year, who was registered with Vaillant when he installed it. The plumbers that came today were both Worcester Bosch and Vaillant registered installers.

I got both sets of details from the Vaillant web site.

I'm not sure how to identify a plumber who is familiar with these boilers if Vaillant themselves aren't capable of ensuring this is the case!

 

[gaswizzard]

The boiler was serviced by the original installer in November last year, who was registered with Vaillant when he installed it.

What checks/part replacement/s were carried out?

The plumbers that came today were both Worcester Bosch and Vaillant registered installers.

Means nothing as you have already explained in you previous post.

I'm not sure how to identify a plumber who is familiar with these boilers if Vaillant themselves aren't capable of ensuring this is the case!

I feel you pain along with many others , most times it's pot luck.

 

[Milleniumaire]

What checks/part replacement/s were carried out?

I confess I left him to it. I didn't have to pay for anything other than the agreed servicing cost so I don't think any parts were changed, at least no non-serviceable parts were changed that would have cost extra.

 

[Bunnyman]

An installer and a repair/maintenance engineer can be a different animal, if you drain the boiler and press the minus button an it shows anything above 0.3 bar the pressure sensors is knackered, I'm afraid the people you got in are not familiar with your unit. I can't believe Vaillant would tell you what you have posted in the thread if so they need there backside kicked. You can try an clean the sensor but I not had much success with that.i think the price you paid reflects the quality of job you had. This problem will reoccur shortly I'm afraid

 

[bell824]

as you are from yorkshire and i do not know any reputable engineer's on here from yorkshire that are fellow bunny's then what i would reccomend for you is get vaillant out to look at your boiler, don't rely on their installer list but instead look at guys that repair these unit's.
sometimes an approved installer is just that, but an approved repair engineer is different.

 

[Milleniumaire]

This problem will reoccur shortly I'm afraid

You're 100% right! I awoke to a cold house this morning with the analogue gauge showing no pressure and the display flashing F.75!

The digital gauge was showing 1.3 bar!

I let more water in, allowing the pressure to reach 1.5 bar and all started working. When I left for work, the digital pressure was showing 2.6 bar. Doh! Back to high pressure readings.

So much for paying £54 to recharge the expansion vessel - a waste of money!

I'll give the plumbers a call today and see what they suggest will be their next course of action.

 

[The831Bunny]

They either over pressurised your vessel or its lost all the pressure they put in.

When they come back get them to change the pressure sensor while they are at it! If they did what has been advised by myself and everyone else you would have had a warm house... You're stressed? I can't take much more

I wonder if you will look back at your origional post when the job is sorted and change your mind

 

[Agile]

sometimes an approved installer is just that, but an approved repair engineer is different.

Its a great pity that manufacturers dont list approved repair engineers!

Its also a pity that owners dont realise that someone who is gas registered may have no idea of how to repair boilers. Installing boilers requires practical skills but no diagnostic skills.

It should be obvious that if the dial pressure gauge shows zero and the digital display still shows plenty of pressure that the pressure sensor is likely to be blocked.

The F75 is produced when there is no variation in pressure as the pump starts.

Its all very simple really, well to me anyway!

Tony

 

[Milleniumaire]

It should be obvious that if the dial pressure gauge shows zero and the digital display still shows plenty of pressure that the pressure sensor is likely to be blocked.

This fact also seems to have flummoxed Vaillant technical support. I have been trying to get through to their Homeowners Technical Helpline today to challenge them on their email response, but it is constantly busy.

As I said earlier, when I asked them (via email) why the two gauges showed different values they simply told me the digital gauge was more accurate. So based on that answer, if the analogue gauge shows zero and the digital gauge shows 1.5 bar, then 1.5 bar is the correct pressure!!!! I did suggest to them that the value of the digital gauge is only as good as the value supplied by the pressure sensor, so if the pressure sensor was faulty the digital reading would be wrong. That was Friday, so it's probably too soon to expect a response from them yet (or they are ignoring me).

 

[Agile]

The digital pressure is only more accurate when the inlet to it is not blocked!

If it still reads when there is no pressure then its obviously blocked and NOT giving a correct reading.

Tony

 

[Milleniumaire]

I spoke to Vaillant technical support a couple of times this week. The first time the guy suggested the pressure sensor need to be replaced, but as the heating has been working fine since the expansion vessel was recharged i.e. no water escaping, no loosing pressure, albeit the pressure is around 2.6 bar when it is working, I called back to ask if this pressure was okay. The response was that 2.6 bar was perfectly acceptable while the boiler was running.

I also spoke to the plumber who had recharged the expansion vessel, explaining that the boiler was still running at 2.6 bar after I'd had to let more water in the day after he had visited. He suggested there may be a problem with the expansion vessel and also suggested that the standard 10l vessel wasn't adequate and an external expansion vessel should be installed. When I queried the difference in the two pressure gauges, he didn't have much to say other than if I wanted him to try installing a new pressure sensor he would, but felt that changing parts might end up being costly. He also suggested that running at 2.6 bar wasn't too much of an issue and we agreed to leave it for the time being.

So, that's my current position. I'm getting different information from Vaillant and I've now decided to just let the boiler run as it is it. As long as the pressure isn't getting too high, then it isn't loosing water, so is not causing me a problem. I noticed today that the pressure was down to 2.2 bar. Maybe this is because it is a little warmer than it has been and so it doesn't have to heat up the water as much.

Currently, my only concern is the "high" pressure, but nobody seems to think this is an issue, so maybe there isn't a problem after all. In terms of the two gauges showing different values, so what - I can live with that providing I'm not having to let more water into the system every other day.

 

[Agile]

The high pressure reading means less until you tell us what the cold pressure is.

Its the amount of increase which indicates how well the EXV is absorbing expansion.

I would never recommend that a boiler is left as "normal" if running over 2.2 bar. Thats too close to the discharge pressure for the PRV.

Do you know if your plumber repressurised the EXV with the pressure maintained at zero?

Tony