Boiler losing pressure

tony3619

So Ive had an issue with my combi boiler for years....it will drop pressure slowly over 2-3 months requiring a top up. Ive never found a leak until today I noticed a small pool of water on top of this pipe (circled in red) 

Any idea what this pipe is for and why would water be released from it? 

Mr.Generous

It looks like an automatic air vent, when the washer dries out it allows the air out, when the water comes through it seals again. A tiny bit of water is ok. BUT air doesn't really get into the system, it's more likely corrosion gasses, so adding a dose of system inhibitor and bleeding the radiators would be worthwhile.

tony3619

Mr.Generous said:

It looks like an automatic air vent, when the washer dries out it allows the air out, when the water comes through it seals again. A tiny bit of water is ok. BUT air doesn't really get into the system, it's more likely corrosion gasses, so adding a dose of system inhibitor and bleeding the radiators would be worthwhile.

Would you say this is likely the cause of my drop in pressure over the last 4 years? Or a symptom from the constant topping up?

ThisIsWeird

Not a symptom. Possibly a cause.
If it's losing water, then clearly it'll be leading to a slow pressure loss. So it's the first thing to tackle.

How is it fitted - soldered or compression joint? Are you up for some DIY?

Is that a plastic cap on the top? If so, you could trying undoing that and adding a smear of silicone grease (NOT sealant!) before screwing back on firmly, but then it won't be 'auto' any more. But no big deal.

Do you have a magnetic filter added to your return pipe to your boiler? If not, it would be a useful thing to have done, and you can also use this to add inhibitor to your system, if there's any risk it ain't concentrated enough.

But, at the moment, the only situation you have is a tiny weep from that valve, and that might be the only issue.

tony3619

ThisIsWeird said:

Not a symptom. Possibly a cause.
If it's losing water, then clearly it'll be leading to a slow pressure loss. So it's the first thing to tackle.

How is it fitted - soldered or compression joint? Are you up for some DIY?

Is that a plastic cap on the top? If so, you could trying undoing that and adding a smear of silicone grease (NOT sealant!) before screwing back on firmly, but then it won't be 'auto' any more. But no big deal.

Do you have a magnetic filter added to your return pipe to your boiler? If not, it would be a useful thing to have done, and you can also use this to add inhibitor to your system, if there's any risk it ain't concentrated enough.

But, at the moment, the only situation you have is a tiny weep from that valve, and that might be the only issue.

I'm not sure how it's fitted I will take a look when I get home. 

So I'm assuming these air vents are not designed to let water out? The property is only 7 years old so I'm assuming it's either been leaking here from the early days (judging by the dried residue visible in the photo,) or this is just a separate development and I still have a small leak somewhere else. I've noticed no stained ceilings over 7 years or anything so I doubt it's on the pipework. 

ThisIsWeird

I can see what appears to be white plastic pipe, so it'll be a straightforward 'push' or 'compression' fitting, the easiest to DIY.

No, it isn't designed to let out water, just air. It has a clever wee float inside it which is meant to keep the water in, but allow the caught air to escape. It's quite common that they do leak a bit, tho'.

If you could take a close-up side shot of its top, we can see if the wee cap is still there. Then we can try just cleaning it up and/or tightening it down. You can slacken it any time to allow out any trapped air - worth monitoring in any case, as any significant qualities of air can point to other issues.

You should be able to fully unscrew and remove the cap for cleaning without water spurting out! But, if it's 'faulty', it may drip slowly.

Definitely sort this first, and then keep monitoring the pressure drop.

tony3619

ThisIsWeird said:

I can see what appears to be white plastic pipe, so it'll be a straightforward 'push' or 'compression' fitting, the easiest to DIY.

No, it isn't designed to let out water, just air. It has a clever wee float inside it which is meant to keep the water out, but allow the caught air to escape. It's quite common that they do leak a bit, tho'.

If you could take a close-up side shot of its top, we can see if the wee cap is still there. Then we can try just cleaning it up and/or tightening it down. You can slacken it any time to allow out any trapped air - worth monitoring in any case, as any significant qualities of air can point to other issues.

You should be able to fully unscrew and remove the cap for cleaning without water spurting out! But, if it's 'faulty', it may drip slowly.

Definitely sort this first, and then keep monitoring the pressure drop.

Surely if water is leaking out it indicates that no air is building up? 

I know most of the pipes are flexible plastic and not copper. Would corrosion be a likely culprit in a system only ,6-7 years old,? Maybe it's the inhibitor?

ThisIsWeird

tony3619 said:

Surely if water is leaking out it indicates that no air is building up?

Water will only leak out after any trapped air has done so. So, with the air vent on 'auto' - or simply leaking - you'll never know if there's air in your system, 'cos it'll be vented out without you knowing.

I have one of these auto air vents, and I keep the plastic screw cap tightened down. Every now and then - roughly annually - I'll tweak it open, and will usually get a tiny, less-than-one-second, pffft as a tiny bit of air is expelled, followed by a momentary 'shriiip' as the water hits the outlet. Water doesn't come out, and I have no idea if it would do so if I kept the cap loosened, but I don't want to take the risk, and I also want to know if there's excessive air in my system - that would indicate other issues. So, I keep mine screwed closed.

All you know at the moment is that your vent does appear to be dribbling water, which it shouldn't be. But we don't know how much, and we don't know if there's also air being expelled. If we don't know if there's 'air' in your system, we also cannot speculate whether you have a corrosion or inhibitor issue.

So, if you could take a close-up pic of your valve top, we can hopefully suggest a way forward.