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– Hold tight. If you’ve been lucky enough
to stumble across this video because you’ve got a
problem with the pressure in your boiler and and the
fact it’s constantly dropping, then lucky you and any second
now we’re gonna get started. I’d just like to remind all of you that if this video helps you
out, then please do subscribe. The links to the cards up here are present throughout the whole
video and even at the end. So it’ll be easy for you to subscribe and find any more information
that you might need. We also share videos and
photos of plumbing disasters that you guys send through to us at our Facebook and Twitter accounts. Anyway, I hope you enjoy the
video and that it helps you out and remember everyone to hold tight.,
honest reviews and advice. So you’ve been noticing
lately that the pressure gauge on the front of your boiler
that looks very similar to some of the pressure gauges that I’ve got going on
behind me at the moment has been dropping down. Now if it goes anywhere
below kind of half a bar, then you know that you’ve got a problem and obviously if it’s constantly
going down all the time or that reckedly you’re topping it up using a filling loop like
the ones that we’ve got going on behind us at the moment, then you’ll know that you’ve
definitely got a problem. Now there’s a few things
that can cause this and we’re just gonna go
through them step by step and also give you a quick idea about how you can maybe fix the problem. I’ve seen a few other
videos on YouTube about this and I don’t really feel like
they’re covering very well. So we’re gonna try and do that now for you and I hope you enjoy the video. So let’s go. You may be aware that
we’ve already done videos on how pressurized heating systems work and it’s quite important to
know the basics of how they work when it comes to finding out why you’ve got a problem
with pressure drop. The main things to think
about are that when cold water is heated up inside a boiler
and inside a heating system, the cold water atoms and
molecules start to move and get very, very excited and
because of that, they expand. They usually on an unpressurized system, you have a tank in the
loft with an expansion pipe that goes up there and
that allows the water to expand up and down without
there being a problem. On a pressurized system, instead of having the expansion pipe, you have what’s called
an expansion vessel. How they work is very simple. It’s very difficult to compress water and so therefore you
have an expansion vessel with a rubber diaphragm and
on one side of the diaphragm you have compressed air that’s
usually compressed to one or one and a half bar and on the other side you have
your heating system water. So as that water heats up and expands, it gets more and more happy, it can expand into the
easily compressed air without letting air
into the heating system because there’s a rubber
diaphragm in the way. So make sure that your heating
system is nice and full of water at all times,
you have a filling loop that fills up the cold water
from the cold water main system and make sure that everything’s okay. It’s worth noting as well
that the filling loop is not in all the time, okay. When you filled up the system,
when you’ve done anything, you should turn off both
the valves at each size and remove the filling loop braided hose and just hang that behind the pipe. The main reason we do that is because if you’ve got a problem
with one of the valves, you could overpressurize the
heating system and actually pressurize the whole heating
system up to main’s pressure. So now you’ve got a basic idea about how a pressurized
heating system works. Let’s look at problem number one that could cause a pressure drop. Firstly and most obviously of all, you could have a leak on your
heating system somewhere. When it comes to finding
leaks, the best thing to do is pop around all the
radiator valves for a start and just make sure
there’s no leaks on them. Make sure you lift up the heads as well to make sure that there’s no
weep on top of the valves. Make sure that the compression fittings on each side of the radiator valves are nice and tight and
there’s no water anywhere. Just go around, run around with your hands and make sure that you’ve
got no leaks there at all. That’s number one on the list. Try and stop the leaks. If you find that you can’t
find any leaks anywhere, always look out for sort of dark brown patches on the ceiling. They can indicate leaks. After that, you’re into the gnarly world of pulling up floorboards and
having a look under the floor. Things like that can get pretty horrible. So that’s number one. You might actually have a
leak on your heating system. Number two, most modern combi boilers have what’s called
automatic air vents on them. Now they’re great for when it
comes to venting a system out. Everything gets vented automatically and it works brilliantly. But they can cause problems
if the heating system hasn’t got an adequate
amount of inhibitor in it or if the pump setting is
set too high for the speed. Let’s go through both
of those quickly now. What an inhibitor does is stops the water from reacting with the
inside of the radiators and the inside of the components of the heating system itself. If that’s not in there,
you’ve got normal water going up against the insides of a radiator and causing horrible things to happen. Many, many months ago
I started an experiment with two jars just like this, one with inhibitor in it and
one with just water in it and then popped about 10 nails in each and I think you can see the difference. If I just pop these down so
you can have a closer look at them, you can see the
different state in the nails and if inhibitor is not
inside your radiators, that’s exactly what’s
gonna happen to the inside. Now, another byproduct of this is not just sludge and
rust that goes around and stops a heating system
from working properly, it’s also hydrogen and other gases. What happens is the hydrogen
can work its way around to an automatic air vent and the automatic air
vent’s just doing it’s job, it’s just sitting there
having a nice chilled out day, a little bit of gas comes along and it lets it out quite
happily, but what happens then is the pressure drops down on your boiler. So make sure that you’ve got a nice amount of inhibitor in your heating system. We’ve done a video about how to do that and that’ll be appearing
in the card right now. The next thing to worry
about is the pump speed. Now the problem you have is if the pump speed is set
too high and the water is not getting away from
the pump quick enough, it can do a thing called
cavitation, which is what happens where the pump impellers
themselves split the water and air up and then you
again create hydrogen. So turn your pump speed
down, make sure you’ve got an adequate flow around the holder system and that should stop that from happening. Now obviously the hydrogen
has to escape somewhere and guess what, it goes up to
that naughty little automatic air vent again and drops
the pressure in the system. So there are the other
things you’d look at if you’ve got a problem
with a pressure drop on your pressurized system. The last two things to
look at and unfortunately the most common are problems
with the expansion vessel and also problems with
your pressure relief valve. Let’s have a look at the
expansion vessel first. Like we described earlier
on, the expansion vessel allows the hot water to
have somewhere to expand to without pressurizing the heating system anywhere above what is a safe limit. Now, if the rubber diaphragm ruptures and let’s face it, it is
actually a moving part, then water will go into that, the air will get into the heating system and get taken out of
the automatic air vent and basically what you’ll end up with is an area of no expansion. Now, you’ll probably think that’s gonna make the
system pressure go up. That is kind of true, but
only for a little while. What’ll happen is is the system
pressure will go up and up and up and actually force the
pressure relief valve to open. The way to know that
if you’ve got a problem with your expansion vessel
is to find what looks like a bike pump connector on the
top of it or on the side, press that and unfortunately
you’re probably gonna release all the air out, but if
water starts to come out, then that’s a bad thing, okay, and you’re gonna need to put
a new expansion vessel on. If you don’t find there’s
any water come out, it might’ve just lost its charge through that straighter valve
and you can get a bicycle pump and repressurize it and
then use a pressure gauge to make sure that it’s pumped up to one or one and a half bar. Another thing I’d also say
is a lot of combi boilers only have an expansion
vessel that accounts for the expansion of the boiler itself and doesn’t account for the
expansion of the radiators. I always say it’s a great idea if your plumber’s in and
he’s putting a new boiler in, ask him to whacker a moat expansion vessel somewhere else on the heating system, usually in the airing cupboard and then you’ll halve the risk
of there being any problem with the expansion vessel
or the pressure relief valve ’cause you’ve got so much
more expansion space. Pressure relief valves are very simple. All they are is a rubber valve with a certain set spring
on the back of the valve. When the water gets up
to a certain pressure, the pressure pushes on that spring and then dumps the water
at a safe location outside. They usually run with a
little 15 mil copper pipe that sticks out the
back wall of the boiler and usually the outlet is
behind a hedge or something so you can never see
them running or dripping and let’s face it, most
homeowners aren’t gonna be looking for that anyway. So if you’ve got a problem
with the expansion vessel, the pressure is gonna go up so much and it’s gonna start dumping
out the pressure relief valve and then your pressure
drop will happen that way. Now a problem you can
specifically get with the pressure relief valve is again
that it is a moving part. The fact that you’ve got a
spring on the back of the valve will mean that it is a moving part and it’ll get weaker and weaker over time and eventually 50% of
pressure relief valves will fail after about 10 years and what happens is they’ll
start to slowly drip out and you’ll slowly notice the effect if you’ve got a leak on the system, but of course the pressure
relief valve’s piped up to dump that little drip outside
where you’re not looking. So a good idea is to just pop outside, find that little 15 mil pipe and just run your finger under
that and see if that’s where. If it is, then you’ve
probably got a problem with the pressure relief valve and you’ll need to get a
plumber out to replace it. So there we go. I hope this video’s
given you a better idea about the problems you can have when it comes to your
pressurized heating system and why you’re getting a pressure drop. There are a few reasons. Let’s face it, the most common
are the expansion vessel, the pressure relief pipe, or obviously a leak on your system. One thing I would say,
it’s always a good idea just to top of the inhibitor
in the heating system if you’re not sure anyway and periodically ask
your plumber to come out and just do a nice little
health check on it, drain the whole heating system
out, fill it all up again, pop a couple of tubs of inhibitor in there and your system should be nice and happy. Also at the same time,
if you haven’t got one, ask them to bang a magnetic filter on the return to the boiler and you’re really halving any
of the problems you might have just through the running
of the heating system. If you need any more help
or any more information, pop over to our website, Facebook, Twitter, give us a subscribe. Mr. G, my cat will be over there. He loves to be out that place. Anyway, I hope you’ve enjoyed this video. I do hope you subscribe and remember everyone, once
you’ve got all that sorted out and you’ve figured out why you’ve got this pressure drop
going on, to hold tight. See you later everyone, buh bye.,
honest reviews and advice.

About Bill McCormick

Read All Posts By Bill McCormick

100 thoughts on “BOILER KEEPS LOSING PRESSURE – WHY AND HOW TO FIX – Plumbing tips

  1. The white expansion vessel, you mention to pump it up. If its full of water, do you need to drain it first? If so, how best to do it? Thanks.

  2. You are amazing! Wish there were more professionals like you in the business! Thank you for sharing your knowledge!

  3. If the gas was stopped into the property but the boiler remained on would this mess it up?

    A friend rented out his home, it's pressure bar was at 3 when he finally saw it. So got it back down but now it drops below 1 and have to push it up manually.

  4. On some boilers the heat exchangers leak and it drips to condense !!
    Ps..the expansion on an open system is taken up by the cold feed pipe..
    You cant adjust the pump speed on a lot of combis…

  5. Still making videos today, plus you can follow my VLOG channel here: FANKS! ❤

  6. Excellent video. Videos like this educate people so that when they get a tradesman in they are more clued up and far less likely to get told a load of rubbish.

  7. My condensing boiler was losing Pressure, it was neither of the two faults mentioned. It was the boiler heat exchanger itself leaking. The water was disappearing down the condensate drain pipe. Not visable without taking the covers off. The clue to this being the fault is when the boiler is hot during the day the leak plims up and no water is lost as soon as the boiler goes off and cools down overnight the leak opens up and water is lost.

  8. Nice presentation and good advice. Worth pointing out though that the expansion vessel air pressure (1 to 1.2 Bar) is normally quoted for COLD condition. It shouldn't be pumped up and the pressure measured when the water is hot.

  9. Another point – the PRV can develope a leaking seat, as it is contact with acidic/particle/general muck from the primary boiler water. This can be especially prevalent where the PRV has actuated due to over-pressure. When the pressure has reduced and the valve closes again, bits of grit are left on the valve seat which can fail to seal properly leading to a permanent dribble.

  10. Awesome video! Quick question, before checking or re-pressurising the expansion vessel in a sealed heating system, is it important to have no pressure in the system or does that not matter? Thx

  11. I don't have an expansion vessel or tank and my heating keeps losing pressure but with no leaks that I can see…I'm assuming the system is just dumping the water to an overflow maybe?

  12. We have a warm solution radiant in floor heating system. I have a thunk on the top of the expansion vessel and a twang on the bottom. Is it possible that the filler valve is slowly leaking air? How could I treat the valve seal to stop bleeding air out of the vessel? Thank you

  13. Links to the tools I USE EVERYDAY in the description above! Plus Follow my Vlog, TimesWithJames

  14. Main heat exchanger could be leaking through the condensate sump and be invisible. Also plate heat exchanger could be split causing cold mains to get into the circuit. Also filling loops are removed because of water regs. Also sludge in systems only builds up due to fresh aerated water constantly getting into a system which in turn speeds up any chemical reactions. Don't get me wrong inhibitor is belts and braces but a well designed and maintained system should never produce sludge. Ive drained plenty of ancient systems that were clean, My father's system is 45 years old has never had any chemicals added and when I drained it last year it was crystal clear. I suggest you re do your experiment but completely fill the jars so no air is in them. But apart from that some good advice.

  15. Hi I`ve had this problem. The guy who fitted the boiler and radiators said no inhibitor was required. Maybe I should put some in. It`s about a year since installation, is it too late or shall I go for it.

  16. My neighbor recommended me for her friend, because she had a problem of her gas boiler mysteriously loosing pressure. On Sunday I will go there and check, maybe I will be able to fix it. Gosh, I haven't had many chances to work on heating systems, except in my own house, witch has become now sorta like my own learning grounds. Well, if there is a simple leak on system, or if there is simply bad vessel of Relief vale, I might as well get lucky. I'm learning everyday. I'm surprised that a middle aged woman is confident in 19 yo self thought plumber wannabe, in fixing her boiler. This video is going to be my guide. thanks a lot James.

  17. My central heating keeps losing pressure, topping it up everyday. No leaks from the rads, I have even lifted up the floors. No leak from the PRV. The expansion tank is fine too.
    Any ideas, anyone????

  18. What about sudden total loss of pressure? Eg it's fine for months then next all pressure gone, then fine for months and again sudden and total loss of pressure….

  19. This video was made in 1950 before combi-boilers. It was originally in black and white but was coloured using the Disney colour converting system.

  20. Great video and lots of ideas for tracking down problems. I'll speak with my plumber and make some suggestions!

  21. Our tanked boiler keeps getting fault 9, where the heating cuts out and fault 5 where there no hot water. Often have to reset it 5+ times a day. Any ideas what it might be.

  22. I had two yesterday that told me a toilet bowl leak was condensation. It's a leak that seems to get worse the colder it is. I always thought condensation was a heat problem. And for the previous twenty years there's was no leak. I'm suspecting it's some kind of insecure pressure connection that contracts in cold weather

  23. Please consider subscribing – Uploading still today!
    Please Follow my Vlog, TimesWithJames

  24. i got a hallsted boiler does the opposite ,it should sit at 2bar but when the gas heater kicks in it will rise very slowly until the next time the boiler kicks in then it will rise again and this keeps going everytime the boiler kicks in .The pressure bar rise to the red marked 3bar when the boiler will shut itself off to stand by mode in red flash light why.

  25. doesnt work for me, water just pisses out the bottom. They should design these boilers to be much easier to use with the need for keys and getting water everywhere

  26. Hi. My boiler needs a steady topping up, because on the morning the gauge is almost at zero. I top it up a bit, and then after a while, whilst it's on, it's starts to give a bubbling noise and the pressure goes into the red. No apparent leakage. Should I be conserned?

    Thanks in advance.

  27. Hi, Ive got a water leak from the pressure valve, I only noticed it when I was increasing the pressure after bleeding the rads, the leak stops (although Im not sure if it stops completely) when closing the valve. Getting an engineer out next week to look at it, do you think it is a big job? Got homecare policy but I know what they can be like with exclusions ( they dont cover rad flush but I intend to do that myself).
    Liked the video btw. Thanks.

  28. Excellent video as always. Got a Worcester Greenstar 30si, That keeps losing pressure, got to top up every day, and put air in vessel. So far so good, run boiler after 10mins water leaks from prv outside pipe. And when boiler cools pressure is down again. Oh and water comes out of vessel. And when boiler is on, the pressure gauge goes way up to 2bar and over sometimes. Is it the prv or vessel at fault. Thanks for reading, feedback Welcome 👍

  29. Another tip for combi boiler pressure drops. After trying all the above, if you’re still getting a drop you can fit 2 isolation valves under the boiler on the flow and return. Isolate this for 2 days and check pressure after. If it drops then it’s the boiler, if it holds and then drops after you open valves then it’s the pipe work.

  30. Hi, we are looking to replace an old boiler and water tank with a modern combi boiler do you have any recommendations thanks

  31. Please can you help with this. The boiler pressure is constantly running too high, way past the green. When the system is cold it is still too high. The expansion tank does have air in it. Two radiators do not heat very well, one is warm the other is cold. If you close either one down using the thermostat the other will warn up. Is this related to the boiler pressure. Thank you.

  32. Imo this video was rushed talking to quickly to get all the info in
    And a lot of the info would go over the heads of a lot of laymen watching this video

  33. It's a pity what you said about cavitation creating loose hydrogen isn't true – it'd be a far cheaper way to generate hydrogen.

  34. Cavitation does NOT cause atoms to split. It causes water to boil, but the steam readily collapses on the impeller again. No gases are produced that are vented away. Cavitation is bad, and will wreck the impeller, but it doesn't cause a drop in system pressure. A drop in system pressure can cause cavitation, not the other way around.

  35. Plumber Parts how do I find out the correct multibloc pressure valve pressure for a worcester boiler pressurised system?

  36. Thank you this was so helpful, living on my own after 23 years of marriage, starting to get the hang of things 😄

  37. We've got a brand new worcester Bosch cdi 32 combi, this is constantly losing .5 bar weekly, our installer says his tried everything. Tested the rads, checked for leaks no obvious signs. He came yesterday and re-adjusted air vent, cus our boiler was making a very strange noise like it was 40 years old not 4 months, we are now gauging whether this helps. We wont hold our breaths

  38. Good one "Hose Mourinho".
    I have completed a check of all my radiators, no sign of leakage and removed cover on the boiler, no apparent leaks and looking very dry. The pressure is dropping and radiators appear to be outputing more heat than is indicated on the digital reading on the boiler. Do you think it could be PRV or is something else going on.
    Thanks for posting this excellent and say hello to "Mr.G"
    Greetings from Glasgow

  39. Many thanks for these videos, really helps narrow down the problem.

    Tiny bit of dirty water came out the Schrader valve and not much air of a 15 year old combi system.

    Symptoms have been (for sometime): CH only works after running hot tap, constant filling of water (where does the water keep going?) to bring pressure up almost daily since xmas.

    Re pressurising expansion vessel via pump the weekend, it appears to be losing about 0.1 bar per day. A biasi M90F looks like I have to remove the boiler to replace the vessel. Damn!

    Thanks again.

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