Frequently having to top up water pressure in Vaillant combi.

[Johnking]

Hi,

I have an ageing Vaillant Turbomax 282e. Recently it's started requiring the water pressure to be topped up much more recently. Reading around it seems like there are two main possiblities, a leak in the pipework, or something I don't yet understand to do with air pressure in an expansion vessel. Can anyone help me figure it out? No signs of leakage in the pipework, but I did change a thermostatic valve last winter.

 

[muggles]

Top it up when the system is cold, then watch the pressure gauge as the system heats up. Does it go above 3 bar?

 

[Johnking]

Top it up when the system is cold, then watch the pressure gauge as the system heats up. Does it go above 3 bar?

Thank you for replying so quickly!
I topped it to 1.5 (it had gone down to 0.9 since last night), and then set the boiler thermostat to 7 and switched it on. Temp climbed from 30deg to 70deg over about 15mins and pressure climbed to 3.1. At that point I turned the boiler thermo down to 5 and the boiler switched off.

Is this informative? Is it safe?

 

[footprints]

I don't want to butt in on muggles post but, the next question as I am on and see you are too, the next thing I guess he will want to know is does water escape from the discharge pipe outside run in 15mm copper usually. Because at 3 bar + the safety valve cuts in and discharges the pressure outside.

 

[Johnking]

I don't want to butt in on muggles post but, the next question as I am on and see you are too, the next thing I guess he will want to know is does water escape from the discharge pipe outside run in 15mm copper usually. Because at 3 bar + the safety valve cuts in and discharges the pressure outside.

There is a pipe out the wall behind the boiler, is that it? I did not look, and I stopped the boiler as it got over 3.0 because I was concerned. I will rerun the test and look for water.

 

[footprints]

Be careful that water will be hot and under pressure.

 

[Johnking]

OK, this time it got to 3.2 before turning the gas off (pump still running of course). The pressure reached 3.2 but there was no water from the discharge pipe.

 

[ianmcd]

you do have an expansion vessel problem

 

[footprints]

It really should not get to 3 bar, it does sound like your pressure vessel is shot.
I assume the pressure has not gone right down just back to 1.5 again.

To explain water expands when hot, this increases pressure in the system. In an open system it expands into the loft tank, in a closed system like yours it has to be absorbed somewhere. you have a pressure vessel with a diaphragm down the middle, one side is open to the water the other is pressurised with air (or some other gas) water cannot be compressed but gas can, so the diaphragm pushes into the gas side like a cushion as the water heats.
When it cools the diaphragm moves back. If the air pressure is lost from the vessel the diaphragm goes right across when you fill the system and so there is nowhere for the water to expand to other than the safety valve.
It sounds like you are starting to loose that cushion of air and when really hot the water pressure is venting.
Sometimes a vessel can be re-pressurised but unless someone has deliberately let the air out usually it will leak away again.
Call an engineer he may be able to pump up the air side (with the water system de-pressurised) and reset it but chances are you may need a new vessel.

 

[Johnking]

Thanks both. It hasn't vented so far as I can see, but of course I've never looked at that pipe before. I'll call an engineer (there's a great one in London who's been to it before). How much is an expansion vessel? Is it a lot of work to fit?

But more importantly, is the system safe? If I keep the thermostat on the boiler set low I guess it might not get so hot and thus less pressure?

 

[ReganAndCarter]

I've got one of these excellent boilers. To replace the EV, the boiler has to come off the wall as it's down the back. Your engineer may be able to re-pressurise the EV, but as the boiler is getting on, it may need re-newing. Rather than remove boiler, I fitted an external one on the ch return pipe near boiler. Much easier and cheaper.

And don't be tempted to change the boiler if it is otherwise ok. They're one of the best boilers ever made in my opinion, and with regular maintenance will keep going.

 

[Johnking]

Me again... I did some further observation because I would rather not call an engineer unless it's certain.

I ran the heating twice more, with the boiler thermostat at its usual position, 4. In both cases the pressure went up to 2bar, from its baseline cold pressure of 1.5.

I also located the expansion vessel and gave it a tap - it sounds hollow.

I'm wondering if I have topped up the pressure too high (1.5) and also lost some air pressure in the EV. The manual says the factory charge on the EV is only .75. I can't find any instructions about topping up, so I have to assume that is the working pressure.

So before I call an engineer I thought I'd release the boiler pressure, check the EV pressure with a car foot pump and top up if necessary, then repressurise to 1.2 bar, which is what it always used to be.

Anything wrong with this plan?

 

[Johnking]

I've got one of these excellent boilers. To replace the EV, the boiler has to come off the wall as it's down the back. Your engineer may be able to re-pressurise the EV, but as the boiler is getting on, it may need re-newing. Rather than remove boiler, I fitted an external one on the ch return pipe near boiler. Much easier and cheaper.

And don't be tempted to change the boiler if it is otherwise ok. They're one of the best boilers ever made in my opinion, and with regular maintenance will keep going.

Oops, was typing, missed your post. Yes, the ex-Vaillant guy who saw it last year said as much about the boiler, he was quite passionate about it and the most fair and professional person I've ever had found in any trade. You can find him of you search for Vaillant service London.

Not much room for an external EV, works have to be mounted behind a kitchen cupboard or in the underside of a worktop if it has to be near the boiler. Hopefully it might be a pump up job.

 

[footprints]

If you want to check the vessel pressure it has a small schrader valve like a tyre on the vessel the water side should be depressurised when checking. Put the gauge on and see if it is the .75 you quote. It pumps up like a tyre I used to have a pump with a 6 ft hose for doing it with my foot, but a quick arm work out will do it!
The system is then represdurised to around 1 bar.

This assumes you can access the vessel without removing any room sealed case from the boiler.
Not sure if your case is decorative or is sealing the combustion chamber off hand.

Many can be accessed from the top without dismantling anyway.

 

[ReganAndCarter]

This assumes you can access the vessel without removing any room sealed case from the boiler.
Not sure if your case is decorative or is sealing the combustion chamber off hand.

It would be ok for OP to remove case. as it's only a cover, not sealed on the Turbomax Plus.