[Closed] Plumbing - what's this thing?

pressure release valve

It's an air vent valve

Is it used for bleeding things or as an emergency vent?

It's an automatic air vent - if you loosen the red cap any air should automatically bleed out. It has a float inside and should seal off before any water comes out although sometimes you get a dribble. If there's more that a dribble it's defective!

Ok. Good place to start trying to get air out of the system? It works overall, just noisy pump due to bubbles.

we used have low water pressure to the house which caused this.

You need to loosen the red cap for it to work, but in my experience that particular kind are a little unreliable. You shouldn't be getting air INTO an unvented system, it's higher than ambient pressure. Circulating gas could be caused by corrosion of radiators so if you've never had inhibitor added to the system or have done much topping up, that might be your problem.

Run the heating and lightly tap the air vent with a mallet might help force it to vent the air, as will cycling the pump. You can unscrew the cap completely, water won't come out.

Hm, undid plastic cap, nothing seemed to happen. Guess I will just run the heating , open up all the rads on the top floor, bleed, then repeat often. Eventually the bubbles should end up on the top floor when pump isn't running...?

If it's an unpressurised system with a header tank the ballcock may be stuck so you're effectively running out of water and won't have much pressure in the rads anyway.
If it's pressurised check your system pressure it may need topping up via the filling loop.

What temperature is your boiler set to, having it too high can "boil" water introducing air to the system. A mate of mine had a business selling a vent device (£200-ish) and he said boiler setting was quite a common source of air in system. I can't verofy this but it sounded believable

It's an auto air vent, and after a month it will do one of two things, either leak water, or not vent air, and nothing in between 🙂

Dunno about that thing, but when bleeding radiators you should do it the the pump [b]off.[/b] Otherwise you can suck more air into the system rather than letting it out.

having it too high can "boil" water introducing air to the system

I'm no physicist but I wouldn't have thought you could create air from, uh, thin air in a closed system. Water vapour, maybe.

Cougar, apparently corrosion can generate gas and also bacteria.

System is closed, pressure is OK although it has leaked to zero pressure in the past before I put leak stop in it. Boiler is set to max as per it's instructions.

Leak stop could I guess stop the auto vents from working...

Boiler is set to max as per it's instructions.

If condensing boiler that's a horribly inefficient way of running it.

There you go Cougar:

If condensing boiler that's a horribly inefficient way of running it.

Why?

Pretty sure the instructions tell you to run it at max.

If running it at max 80c. Most boilers would hate a delta of 25c - 30c for what it would need to reach dew point amd be condensing and at optimum efficency.

So it's the delta that counts. Ok.. how to measure that?

Temperature probes on the flow and return at the boiler. Depending on mod of the boiler though it might tell you 😉

There's far too many variables at play here to decide that someone on the internet shouldn't run their boiler at Max.

The system using a thermal store being one of them, you could waste a shit load of gas by not quite getting a thermal store up to temperature.

Temperature probes on the flow and return at the boiler. Depending on mod of the boiler though it might tell you

Wouldn't tell you anything of use without also gas rating the appliance, it'll modulate the amount of gas it's burning depending on the temperature rise and difference between the flow and return temperatures.

With a low enought temperature return the boiler will condense regardless of gas rate. While it may try and modulate the amount of gas if you've got system issues. Not bein correctly set up nov about if the boiler tryin to modulate the gas will help. S.53 for example.

My point being if its a condensing boiler it shouldnt be run at max temp unless the customer didnt want to upgrade the radiators when changing from 11c delta to 20c delta. More often than not though the rads wouldve been over sized anyways.

If you can run the boiler low enough itll condense regardless of the delta.

The system using a thermal store being one of them, you could waste a shit load of gas by not quite getting a thermal store up to temperature.

could you expand on that, please? I have a condensing combi with inbuilt storage and run the CH to get the right delta, but set the DHW for the temperature I want the hot water at.

It's a different set up to a combi boiler. A heat only boiler is used to heat a large store of water, the store of water is then pumped through a heat exchanger to heat the domestic hot water, or pumped out of the store to heat the radiators.

Mine is not a combi boiler.

So anyway I poked something down the hole under the red cap and got a load of air out then some yummy central heating water in my face.

Lots of bubbles still in the system though despite having bled the rads a few times, getting less air out each time.

The bubbles don't seem to be at the top of the system though. The pump is at the top, and when it starts up it's silent, then after 30 seconds you start hearing bigger bubbles, then after five minutes or so the bubbles seem to be small ones fully distributed around the system.

I think the pump is pulling water straight up from the boiler then through all the rads going down through the house to the ground floor then back into the boiler.. that sound right? If so, the bubbles are in the boiler?