Vailant Boiler Issue

[alig301]

Hi all,

I have a bit of an issue with my Vaillant TurboMAX Plus 837 combi boiler.

The system keeps dropping pressure. There is no leak, the water is being ejected via the 3 bar pressure relief valve but only when the water is hot. I have topped the boiler up at night (to 2 Bar) after it cools and in the morning the pressure has remained and no water has been ejected but when the boiler is on, the water pressure doesn't get above 3 bar but water is ejected even when the pressure only rises to 2 bar. There is air pressure in the expansion vessel.

The PRV is the prime suspect, but just wanted to ask if anyone had any other thoughts, just because it only passes water when the water is hot.

Thanks in advance

Al

 

[Dan Robinson]

Expansion vessel.



Perhaps someone would write a faq, then we wouldn't have to answer the same questions every day !)

 

[Blagard]

Expansion vessel.



Perhaps someone would write a faq, then we wouldn't have to answer the same questions every day !)

They already did it is at the bottom of the FAQ on Boilers Also the potential solution to simply repressurise

 

[alig301]

Dan,

thanks for the almost instantaneous reply, can I ask why you say the expansion vessel please.

Regards
Al

 

[muggles]

It'll be the expansion vessel, probably coupled with a slightly blocked pressure gauge leading you to think the pressure isn't rising beyond 3 bar when it actually is.

 

[alig301]

When the pressure doesn't rise above 2 bar on the meter it still leaks when the water is hot, but when the water is cold it will happily sit at 2 bar all night with no leakage.

 

[Blagard]

See FAQ 15 in Boiler & Central Heating then item 3 in it.

//www.diynot.com/forums/plumbing/boiler-central-heating-faqs.175736/

 

[alig301]

If all the air in the PV has gone, the water has nothing to squash and the pressure will keep rising to 3 bar which will activate the PRV and water will exit through the wall.

But there is air in the Pressure Vessel. The air pressure is at the required 0.9 Bar

 

[Blagard]

Yes but not enough air! - It is probably almost empty What little space is left is quickly taken up then your pressure goes up and the PRV leaks

 

[alig301]

But that is what the pressure needs to be , Surely if I put in more air increasing the pressure then it will force the water out so leaving the correct amount in the PV

 

[Blagard]

But that is what the pressure needs to be , Surely if I put in more air increasing the pressure then it will force the water out so leaving the correct amount in the PV

For goodness sake, read - //www.diynot.com/forums/plumbing/faqs.37170/#251090 number 1 You should have by now anyway if you followed the earlier link!

Edit:
And when you have learnt how to properly re-pressurise the PV and if it turns out not to be the problem you can move on to the next thing.

 

[Bunnyman]

As he said, drain ur boiler to check exp vessel pressure.

 

[alig301]

All sorted now. Thanks for all who replied. Just for the record it was the PRV

Regards
alig