Vokera boiler expansion vessel problem

[psaffrey]

Hi there,

I have an old Vokera 80 SP which can't control its pressure. If I switch it on, the pressure goes up to 4 bar very quickly and leaks out quickly as well.

I got the British Gas guy out to have a look at it and he said that the expansion vessel needs to be filled. However, the fitting of the boiler is such that he couldn't get to the valve to top it up. He was a bit grumpy about it and told me I should just get a hammer and bang a hole in the boxing around the boiler to give him access. I was somewhat reluctant to do this and so he left with the boiler still unworking.

After he'd gone, I found that I was small enough to squeeze around the boiler and get to the valve. However, I'm now a little unsure about topping it up myself. I know I can just use a bicycle pump to fill the valve, but this page:

the bottom) says "The most important thing is to do this while the system is de-pressurised and open (so that the displaced water has somewhere to go)". How do I make sure the system is de- pressurised and open?

Peter

[Ed Sirett]

By opening (one of) the drain point(s). However IME pumping a vessel is unlikely to cure things for very long.

[psaffrey]

I'm planning on replacing the boiler within the next few months - I just need it to last that long.

Are the drain points usually under the boiler, or elsewhere? Will that drain the whole system?

Thanks,

Peter

[<me9]

I was expecting to have to add an external PV about 3 years ago on a 10 year old boiler. I pumped it up and it has lasted fine. It's worth a try, it costs little, and if it doesn't work for long, a new PV can then be fitted.

[psaffrey]

I'm having some difficulty locating my drain points. I've checked under the boiler and around all the radiators. There isn't any exposed pipe work elsewhere. I know drain-points are usually at the lowest point, but I'm in a basement flat and a lot of the pipework is in the walls.

Can I just drain some off from the top of a radiator and do it that way? If the pressure in the system is very low anyway, can I pump into the expansion vessel without an open valve?

Any ideas appreciated,

Peter

[Jim Alexander]

Well yes and no. You need to drain off several litres and not lot will come out after the pressure drops.

Since water is incompressable that will not work. You will get pressure but no expansion volume. However if you do a few iterations of pumping up and releasing pressure, through the rad if that's your way, you will sort of get there.

Jim A

[Jim Alexander]

Then when you have got your approx 1bar or whatever is the specified expansion vessel pressure, you need to add water until the specified pressure is indicated on the gauge. Got a filling loop?

Jim A

[psaffrey]

Yes. It doesn't point downwards, but it does attach to the system. Can I just drain from there?

Peter

[Jim Alexander]

no because it has a non-return valve fitted

Jim A

[psaffrey]

Thanks for all your advice. I guess I'm arriving at a (rather half arsed) solution:

- Loosen a bleed valve on a radiator and put a pot under it, it will let out some water.

- Pump into the expansion vessel, which I presume will force further water out of the bleed valve. Keep doing this until I achieve about 1 bar on the expansion vessel (that is the right pressure, by the way, according to the manual for the boiler)

- Close the bleed valve, and repressurise the system from the filling loop.

Does that make any sense?

Peter

[Jim Alexander]

Yep, more or less. And remove the boxing now in preparation for your new boiler.

Jim A

[Jim Alexander]

Ha. Now you say. Look in the boiler manual for a reference to a PRV or pressure release valve. It should be connected to a pipe that goes outside. When you operate the PRV knob or lever, water pressure will be released via the PRV. Easier than using the rad bleed point.

Jim A

[<me9]

As long as it re-seals afterwards.

[John Rumm]

Good advice in general, but in this case if the pressure has been going up to 4 bar frequently I would say that has been well tested by now! Once more shot will probably not kill it.

[Ed Sirett]

Agreed. It's one of those things where there's a difference in the best approach between a pro and a diyer. In my case the cost of making a another visit because pumping it up outweighs the cost of using a new vessel and a few fittings. When it's you own system in your own time then the simple pumping up might just work and save you the cost of the new vessel.

[psaffrey]

The Vokera web page archives all manuals from old boilers, which is rather handy. I would post a link, but it's behind a horrible Flash site.

Anyway, there's no reference to a PRV, but there is a "safety valve", a red tap with "3 bar" written on it. The pipe from it seems to run in the right direction to go outside, so I guess that must be it. I'll give it a try tomorrow.

Peter

[psaffrey]

Jim A:

Managed to pump up the expansion vessel and it all seems to be working properly now.

I'm really very grateful for your expert advice, offered for free. If you ever have any software problems, don't hesitate to get in touch :)

Peter