Boiler pressure dropping - should I open the valves?

united4ever

Happened for years and my workaround was to adjust the valves to get the pressure to the right level. 

Boiler man came for service recently and replaced a part (think it was the thing that floats inside - forgot the name- he said it was too full of water and replaced it). 

I explained about the pressure dropping and he said the valves should be closed and now he has fixed it the pressure should stay up.

2 weeks later and pressure is dropping. Boiler makes some noise like a WW2 bomber flying past. I think the wind causes this but always  coincides with pressure being too low.

Am tempted to adjust the valves to put the pressure up. Should I do it? Also worried if the pressure drops too low it will stop working and getting it restarted required an expensive visit from boiler man last year.

It's a Volker boiler if that matters.

I have the radiators switched off but always the living room is fully open and controlled by thermostat. (I don't really heat the rooms that are empty all day except for bed time when I put them on for an hour). Dunno if this affects it.

Bendy_House

We need the model of boiler too, and a photo always helps.

And we need to know for certain - not just guess - which valves you are referring to   (A photo of that would be good too...)

And I haven't a clue what the floaty thing he replaced is. Or how it can affect the system pressure.

More info, please.

united4ever

Volker Compact 29boiler below shows the valves that I have turned in the past circled in red.

DB1904

Isn't that the filling loop?

Bendy_House

Thanks u4e - that's very clear.

Yes, if you need to top up your system pressure, then these are, indeed, the valves to turn.

Open one - the bottom one (tho' it doesn't really matter too much) - fully, and then sloooowly open the top valve. Listen to the noise - you should hear a hissss as the water passes. Keep an eye on the pressure gauge, and stop when it reaches 1.2bar. That should get your system going again.

Then monitor what's happening. If your boiler is off or cold, then the pressure should hopefully be at around that just-above 1bar level. Ok, what happens as your boiler heats up your rads? Does the pressure change? Does it go up? If so, by how much. Check it again in a half-hour when your system is 'piping'.

Please report back.

And, how long does it take for the pressure to drop to below 1 bar?

Bendy_House

I still don't know what the 'float' thing was, but the only one I can think of that could lose the system some pressure is, perhaps, the auto air vent?

Do you have an invoice for the work? Does it say anything on there?

united4ever

Receipt here. I might have mistaken what he said.

united4ever

I have been opening the valves for a few years as required as you described. 

This time the boiler man left them closed and said you don't need to turn the valves, leave them closed. However, now the pressure is gradually dropping over 2 weeks close to the level 1 I was wondering whether to just go back to opening the valves.

Seems much worse in winter but I need to do it every few days in winter otherwise it would be down to zero pressure. In spring summer It could ve every few weeks that I tweak the valves. It's hard to get it right so it is the tiniest twist of the valve to get it to the right level.

united4ever

So my son is having a shower now and it has gone to zero. Will wait and see if it goes up when he finishes.

Bendy_House

Ok, the guy has fitted a new Expansion Vessel and a PRV - Pressure Release Valve.

Clearly you had pressure problems before this, and I don't just mean a falling pressure, but almost certainly a soaring one too...?

Okkkaaay, water expands when it's heated, yes? Cool. Yours is a 'sealed' system - it isn't 'open' anywhere. It is normally pressurised to 1 bar when cold. Clearly, when you fire up the boiler, the water is going to become very hot, and it will expand by likely a couple of litres in volume. When it cools down again, the water contracts and it goes back to how it was before.

In what is a sealed system, however, what'll happen when the sealed volume increases by a few litres? The pressure will soar, right up to 3 bar and beyond. That ain't good. So sealed boilers have an 'Expanion Vessel' inside them that will take in this extra expanded water, and then release it safely back to boiler when it's cold. The pressure should therefore remain fairly constant, and not really increase by more than a half-bar or so, if that (they do vary).

So, the EV keeps the pressure stable. When things go wrong, however, and the EV doesn't do its job, what happens? The pressure soars right up and your boiler EXPLODES! No it doesn't, because you have a Pressure Release Valve which opens at around 3 bar and dumps the excess water outside the house via a 15mm copper pipe (worth finding that pipe - it'll be on the wall outside where your boiler is).

Ah, but what happens if a sealed system dumps part of its water?! Yup, when it cools back down, there now won't be enough water inside it, so the pressure will fall to below the 1bar - and your boiler stops working.

So, you top it up - and the cycle repeats...

That is almost certainly what used to happen? But he's replaced the 2 obvious parts.

You still have a fault - your system should not still be losing pressure (ie water).

One thing you can try yourself is to find that copper pipe, and to see if there's water dripping from it. You can also wrap a small plastic bag around the end using a rubber band - see if it catches anything. Let us know.

Also, keep an eye on the pressure - does it remain fairly constant when hot and cold, or does it vary a lot? If so, which way?

Yes, you need to be able to turn that handle a tiny bit - let it top up gently. If you accidentally let the pressure shoot up to 3 bar, then you'll force open that PRV, and it then has a habit of keeping dripping afterwards = a slow pressure drop.

united4ever

Thanks. I am very familiar with the copper pipe which dripped a lot over the past few years when I turned the pressure up by turning the valves. Not happened since the EV fitted since the pressure hasnt been above 2.

So perhaps the best advice is yes  to turning  the valves but make sure it doesn't get anywhere near 3 and force open the PRV.

When I opened the valves I just did both or 1 by the tiniest amount because any more seemed to make it shoot up and then keep going for a minute or two to 2.5. The way you described opening one valve fully  and then the other one slightly makes me worried that opening one fully will send it straight to 3. I find it hard enough with the tiniest turns to get it to stop below 2.

Thanks again