Baxi Boiler Pressure Relief valve

[AnthonyL]

After being disturbed due to other work the pressure relief valve appears not to be sealing and the pressure drops to zero. I can keep the pressure up by cracking open the inlet tap just a tad, getting about 2 bar, but of course water then drips out of the outlet pipe.

Whilst waiting for someone to come and fix it a few questions:

1) Am I causing any problem by doing what I'm doing?

2) What happens if I just let the pressure drop to zero?

3) Is the water coming out just tap water or will there be CH radiator water as well? ie is the pressurising isolated or part of the radiator system?

[Graham.]

On Mon, 09 Oct 2017 10:52:56 GMT, [e-mail] (AnthonyL) coalesced the vapors of human experience into a viable and meaningful comprehension...

The latter, it's the primary circuit. The water you are adding will be diluting the inhibitor, so the system may require redosing.

[Chris Bartram]

You're diluting any corrosion inhibitor and adding more limescale. You may also over-pressurise things. Technically, i think you may be breaking a water byelaw by connecting the radiator system to the mains (semi) permanently.

The boiler will probably refuse to fire up.

It's part of the radiator system.

[newshound]

Once they have been lifted, these valves quite often don't seal again IME. It is the pressurising system for the radiators (and the heating coil in the hot water tank, if you have one).

I would not advise "drip feeding" it by cracking the filling valve because you are losing inhibitor all the time the relief valve leaks, but perhaps with one exception.

If you let the pressure drop to zero, the boiler should trip out leaving you without any heat or hot water. If you (or other occupants) are vulnerable to low temperatures and don't have any alternative heating it is perhaps the lesser of two evils to waste your inhibitor. Explain this to your plumber and they will test (or more likely replace) your inhibitor when they fix the valve.

What do you mean by a drip? More than a bucket a day will be significantly diluting your inhibitor, and also introducing limescale to your boiler, which is (in general) a bad thing. If it is less than a cup a day, and you can get a plumber in within a couple of days, you won't really be doing much harm.

[AnthonyL]

That's what happened, it had to be disturbed when the diverter valve was replaced. The service guy said he'd be back in a few days, that was a month ago - now he says I need to rebook the job!

Oh that's not good.

My wife wants the heating on at night.

Not measured by bucket, it's a thin stream.

Next question - how do you get someone to come out?

Any recommendations for around the north/north-east side of the city of Nottingham welcomed.

[John Rumm]

You are continually adding fresh oxygenated water which will cause accelerated corrosion and limescale deposition in the heating system.

Then the boiler will lock out or just refuse to fire next time it tries to start up.

Its the primary water that flows though the boiler, and the rads.

If the boiler is a combi, then there will be a separate heat exchanger for the tap water. (and that secondary heat exchanger HE is itself heated by the primary water heated by the main heat exchanger - there is normally a diversion valve in a combi which will direct the flow of primary water either through the rads, or the tap water HE)

[AnthonyL]

Thanks.

I mentioned in one of the other posts that the problems started after the combi diverter valve was replaced. So using hot water is going to be an issue even if I turn the CH off?

PS none of the companies I've contacted today have got back to me :(

[newshound]

I *think* combis will normally still give you hot water even if the CH side locks out because of low system pressure. Personally I think they are the spawn of the devil.

Seems to be a common problem, presumably only about to get worse.

[John Rumm]

Alas yes.

You need the primary side filled and at adequate pressure to run the rads or the hot water. When in hot water mode, the diversion valve short circuits the primary loop such that it just flows through one side of the secondary heat exchanger, and then back to the main heat exchanger for reheating[1]. (The cold mains only flows through the other side of the secondary heat exchanger).

[1] Just for extreme pedantry, there are a very small number of combi boilers out there that actually have the tap water HE heated directly from the gas just like the primary one, or instead divert the cold mains water through the primary HE itself in place of the water normally circulated to the rads.

Fixing the over pressure relief valve is DIYable. (as would be replacing it) if you can get to it reasonably easily. Chances are its just acquired a bit of crud / scale / solder etc that is preventing it from resealing correctly. Just taking apart anc cleaning it will probably fix it.

[AnthonyL]

Thanks. I have a man coming this afternoon - arose out of a recommendation from someone I don't know on a local message board I frequent so that should be fun. To be fair the recommendation is from someone who says he runs several properties. I'd like to do it myself but I just know I'll put it all back together and it will be worse.

Whilst I agree that it may be crud the last guy did a few "blow outs" and it seemed to work for a while. The part costs about ?20 and mine is a good 10yrs old.

My main worry know is the amount of fresh water I've introduced to the system as this problem has been ongoing for a few weeks and I understand a complete flush is a slow process.

Any advice on what I should be getting the service guy to check? Presumably all radiator fluid above the height of the valve will end up draining out - fortunately as this is a bungalow that will only be the pipes that go up and down.

[John Rumm]

No need for a flush generally, unless the system has lots of sludge in it, just get them to add new inhibitor when the system is back up and running.

If its a modern condensing boiler, then it might be worth getting a magnetic/cyclonic filter (Fernox TF1, Magnaclean etc) fitted on the return to the boiler if its not already got one. That would trap any particulate material before it can get into the boiler and block or damage the primary HE.

There should be service valves on the flow and return to the boiler. So he will be able to isolate that, and drain just the boiler. The rest of the system can be left filled and untouched.

Just mention to him that you have had the problem for a while and so are not sure what the inhibitor level will now be.

[newshound]

+1

[AnthonyL]

Well he came yesterday late afternoon, part in hand, and after a lot of fiddling with a small allen key replaced the valve, repressured to

1 bar (the last guy went up to 1.5 bar), satisfied himself that the expansion chamber appeared to be operating and gave me instructions to check that the pressure didn't exceed 2 bar with the evening's heating.

He seemed quite disinterested doing anything about inhibitor levels, said he was out of the testing paper (litmus paper?) and I had to push him to run through with me what I needed to do.

So today I drained about 1 litres off from the drain point below the boiler, opened the 'drain' tap upstairs where the pipes go from the back to the front of the house, drained another litre then added 1 litre Calmag Chem Protector, topped up with some distilled water and tightened everything up, put the pressure back to 1 bar and checked for leaks. The water that came out was quite clear.

I'll leave it a couple of hours to settle though I'm not sure if that's necessary then my wife wants a shower.

Not sure if I've done all that is worthwhile. I'd like to just run the pump for an hour but I don't know how to do that (Baxi 105 HE).

[John Rumm]

Don't worry, just let it run for a day, bleed the rads again and top up some more from the filling loop if you need to.

[AnthonyL]

Do I need to bleed the rads? All the rads are on the ground floor of a bungalow and the top up was done on the pipe above in the attic which was filled to just overflowing and then cracked open (bled) after I'd pressurised and water came out immediately.

I guess I'll just check the rads for cold tops and check the top pipe again but otherwise all seems well.

[John Rumm]

Any air that was in the system, or that has come out of suspension from the fresh water introduced will eventually accumulate in a rad somewhere.

[AnthonyL]

Got it, thanks

[AnthonyL]

That didn't last long :(

I bled the rads as suggested the next day.

Yesterday morning the rads were cold, boiler error light on:

Pump Fault or Low Pressure

The pressure was at 2.0 bar.

Switched to off - clicked to reset and working again. Working pressure around 2.3 bar.

This morning my wife come's screaming in shivering, got into the shower and the water was cold. Same fault indication - repeated reset procedure and ok again.

One unsettling thing, when I bled the rads I took the pressure to 1.3 bar - it is now sitting, and not changing, at 2 bar which is a little on the high side.

If the inlet isn't turned fully off this should surely be creeping up

- so why has it risen and is it a factor in the boiler turning itself off.

Just a recap:

12/7 Standard boiler service 09/8 Rads not heating, new diverter valve assembly fitted 10/8 Pressure dropping and leaking through the pipe outside This sort of stabilised until 14/9 no longer stable, dropping and dripping outside 10/10 New prv fitted 11/10 Added Calmag 17/10 Bled system 1/11 Above faults started

[John Rumm]

That ought to be plenty...

(are you sure the gauge is working?)

Tell her to stick her hand in it first to test the water temperature!

Is this a boiler with a built in filling loop or the normal braided detachable type?

If its detachable, and your turn off both taps and detach it, is there any water coming out?

[AnthonyL]

Thanks again for your input John.

The filling loop is braided. I'll have a go at detaching it tomorrow when I can afford to turn the heating off again. But if it was leaking the pressure surely would just slowly continue to rise and the pressure relief valve pipe is as dry as a bone.

I went around the bungalow again and checked/bled the radiators. There is one that spluttered for quite a while and it is the same one that did the same when I bled them a couple of weeks back after putting the inhibitor in.

There is a nice description of the pressure system at

I'm wondering now if there is an issue with the expansion chamber introducing a leak into the system.

Of course the engineer will say it's easy to fit another one but the costs of this boiler are mounting up - what next? Pump? Circuit board? Classic dilema of throwing money at it when getting a new one instead of having it serviced may have been a better option.