Help: Vaillant Combi Boiler - Pressure Top-up Pin (No hand valve)

wingman83

I’m trying to increase the air pressure in my Vaillant combi boiler, as the pressure is currently low.

This particular model doesn’t have a hand valve for topping up the pressure. Instead, it uses a small pin that you turn on and off. In the past, I’ve used a radiator key to operate this pin, and it’s worked fine. However, today the radiator key doesn’t seem to fit—it feels too big for the pin.

Does anyone know how to top up the pressure using this type of pin? Should I try a different tool, such as an Allen key?

bjorn_toby_wilde

The pin looks like it may have been rounded off. Maybe the radiator key has always been a bit too large and constant use has done that.

An Allen key is the wrong tool for the job.

Do you have an adjustable spanner or, failing that, a wrench (pump pliers)?

Something like this? https://www.toolstation.com/minotaur-adjustable-wide-jaw-wrench/p50834?store=AV&utm_source=googleshopping&utm_medium=feed&utm_campaign=googleshoppingfeed&gad_source=1&gad_campaignid=19606290684&gbraid=0AAAAAD-vLcXaKFmijNEB5owOiiHFLdfOx&gclid=EAIaIQobChMIw9zbodWpkAMVWIhQBh3bsQdmEAQYASABEgI_KvD_BwE

WIAWSNB

Having bought this recently - giving away the big one and keeping the two smaller - I can vouch that these are perfectly decent and work well; https://www.toolstation.com/minotaur-adjustable-wrench-set/p21779
I have a cute mini adjustable that's just over 2" long, which is perfect for these sorts of jobs.
Wingman, when you slip the adjustable spanner on to that wee thing, rock it back and forth as you apply firm closing pressure on the spanner's thumb turn, so the jaws close firmly and not sloppily on that pin - it must be a snug fit or it could keep on 'rounding'.
Another method is to tighten the jaw as normal, and then remove the spanner. Use the thumb-turn to add a further tightening tweak to close the jaws a touch more, and then 'force' it back on to the pin.
It must be a snug fit.

wingman83

Thanks @WIAWSNB @bjorn_toby_wilde for your suggestion.

I tried using a 7mm spanner, but it was too big. Then I used a 6-inch wrench and managed to open it slightly to increase the water pressure, though it wasn’t an easy task. Ideally, I’d prefer a hand valve (like a knob), but I’m not sure if one can be fitted.

diveunderthebonnet

Well the valve started off being square SO what i would do is go to my shed and get a 1/2 inch drive socket and a 3/8 inch drive socket and try the base of the sockets on your valve, i bet one of them is a good fit when you find out which size is correct get a cheap extension bar the same size and bend it like a car wheel nut spanner, job done.

WIAWSNB

wingman83 said:

Thanks @WIAWSNB @bjorn_toby_wilde for your suggestion.

I tried using a 7mm spanner, but it was too big. Then I used a 6-inch wrench and managed to open it slightly to increase the water pressure, though it wasn’t an easy task. Ideally, I’d prefer a hand valve (like a knob), but I’m not sure if one can be fitted.

Well done.
The 7mm didn't fit, but how loose was it? Any chance of a close-up showing the spanner on that fitting?
See the very end of the square? Can you scrape and see if there's a screw hole under there?
Do you have a washing machine? Does the supply hose have a blue-levered valve on it? Is that blue handle held on by a screw? Do you have a screwdriver? Do you...
Er, try the blue handle on there for size.
Also worth a spray of, say, WD40 on that end, and a scrape with an old toothbrush - clean off that scale.