Why Does My Boiler Keep Losing Pressure? 

This has got to be one of the best, most informative, well explained, no nonsense videos I’ve ever watched on RU-vid. We’re losing pressure somewhere and this has helped me understand much more than I already did with what could possibly be causing it. Well done sir!

Don't be shy/modest about the presentation - it takes loads of skill to present 36 minutes of video with smooth and clear speech and not have to edit it loads - nicely done. Thanks for lots of good info. Sadly it's true what people say in the comments - a lot of people don't know their job anymore and to be able to work out the problem oneself saves loads of time, money and hassle and it make it easier to identify a trader who does know what they are doing. Nice one.

Hi Roger, your video series is excellent. I’m nearly 60, I am so grateful that my Dad is a very practical guy and gave me a great education in my youth. This has empowered me so much in life, from maintaining my own cars, installing kitchens and bathrooms, to plumbing and electrical work. Sadly these are skills that subsequent generations seem to have missed out on, the number of times I have helped friends and family where so called professionals have been utterly useless amazes me.

Roger, thanks very much for this video, diagnosis is a tricky thing and sharing your years of experience is of great value. I drained my system just over a year ago and after filling it up again the boiler kept tripping out, the pressure kept falling and flooding out of the pressure relief and I had to keep topping it up. I thought it was probably the expansion vessel but, not being a plumber, I wasn't sure. I contacted a few plumbers but none of them were interested in doing an investigation to find out what was wrong. I turned down the temperature on the boiler, which pretty much fixed the overheating, but I have been topping it up every week or so for the past year and a bit. Thanks to your suggestion of pressing the air valve to see if water came out, I was able to confirm that the diaphragm was gone and immediately ordered a replacement expansion tank. It's all fitted now and hopefully my days of weekly topping up are over. Once again, Thanks very much!!

I learnt so much from this that I have to say it was a very impressive presentation. One of the best I've seen without all the gadgets & video aids, and I used to deliver them professionally as a teacher, lecturer and commercial trainer!

Hi Roger, I like your idea of using perfume to find a water leak. About two years ago I had a tiny leak I couldn't find. Boiler pressure would go down just below the normal 1 bar in about a year. I used a stink bomb and injected it into the water system. No problem finding the leak with that terrible smell. Turned out to be a compression joint on a micro bore pipe to a radiator in my kitchen. Seems to me that a nasty smell is easier to find compared to a nice smell. Also a nasty smell gives you more incentive to find the leak quickly.

I know hardly anything about heating systems and plumbing ; but I found your presentation to be extremely informative, entertaining and easy to understand. Many thanks!

An EXCELLENT practical clearly explained presentation. A presentation like this takes real skill and expertise!

Hello Roger. It's really refreshing to listen to someone who knows what they are talking about because they are speaking from experience. A great presentation full of useful and interesting advice. Thank you.

Robert. This material is so comprehensive that helped to understand the dependencies and have broader overview. Really I appreciate you sharing your experience. I have drop of the pressure from 1.8 to 1.1 bar every abot six monts. The instalation is about 3 years old. Boiler with external 200l water container for hot water. So I'm going to start with checking this air pressure compensation container.

FYI Our long term 'leak' was due to the expansion vessel gradually losing pressure. We were searching for a physical water leak around the property for months. Pumped it up and has been fine since.

I had no clue about all of this, but you've done a great job of explaining all of this!

Really interesting . Lovely clear explanations . Nice one

I had the opposite reason with radiator pressure gradually increasing; when the boiler pump for the hot water had failed and would dump the hot water in the heat exchanger back into the radiator circuit. The expansion tank pressure was correctly set.

Really informative video thanks Roger.

Very useful Roger! Thanks

I had my system changed from an open vented to a sealed system about 5 years ago. Never fully understood how it all worked, but I do now. Thank you very much.

Thanks Roger a long video but worth every minute

What an excellent public speaker this guy is. Direct and clear explanations with nothing superfluous. Very rare.

Great Video , you covered all expects of looing pressure and the extra expansion vessel how it would help. Thank you

in holland we normally have expension vessels outside the boiler and since the pressure of the cold water is higher then the boilerpressure youre last solution is the other way around with us. for looking at the condensing part of the heat exchanger: we often uses hoses to connect the condensing part so we fill the heater up high and let the hose hang in a cold way above a bucket.

Thanks, very clear explanations of a complex system.

Brilliant, well explained and easy to understand. Im a plumber with 7yrs experience but that was spot on. Exactly how they taught it at college

Hi Rodger thanks for all the brilliant videos, I m in a Housing association house and my gas boiler was installed in 2014 which is a Worcester combi ,it has taken 10 so called engineers to diagnose that the heat exchanger is leaking, they now have to supply 2 men to remove the boiler from the wall as they have fitted it to close to the ceiling to remove the heat exchanger and replace it. I used to fit boilers years ago in the 1980s and we used to pay a corgi registered (in those days) chap to come and connect it up and issue a certificate, which is no longer possible, Ive been telling the engineers that its the heat exchanger for years but they are mostly clueless. Id name and shame them but not sure if you allow that sort of thing. fortunately the boiler still runs without pressure but I bet the inhibitor has vapoured away through the chimney as steam years ago. I bet the scale protector has clogged up a lot to. currently if you top it up with the external loop which in a rented property they say is my responsibility, the pressure has dropped again by the next day to 0. The last one diagnosed it fine but he still reffered to the boiler as a valiant boiler, I think they struggle to actually read the name of the boiler on the front panel sometimes.

absolutely loved this video, its so informative. if i was to learn plumbing this is the man i'd want to teach me

We had something similar going on in the house in which I grew up. The system was not loosing pressure because it automatically refilled itself, but the relief valve was filling the bucket about every week and the radiators, which had automatic bleeders, were constantly venting a little. The problem was that, since it had a tankless ("combi" in UK terminology) tap water heater, the temperature of the system was set to the top of its range so that there would be enough heat for a decent shower (without that, one would have to turn the shower down to a trickle after a few minutes to keep it warm). With that high temperature, the expansion tank was simply not big enough, so the relief valve was always trickling on and off. A proper fix would probably have been an external tap water heater or storage tank, though a bigger expansion tank would have helped. We just lived with it the way it was.

Wow! so much knowledge in this one video. So much invaluable information. Thank you for sharing!!

Extremely helpful well explained.👍

Roger, learned a lot more to help my DIY plumbing. As ever, very clear description and summary. I think this is well worth some Night School certificate! Thanks .

Super helpful video! One to keep for those moments to jog the memory. We've been living at our home for 3 months now and I must have topped up the boiler with water 4 times.

i was able to follow my pressure issue to the overflow pipe and fix it, thanks to YOU

Thank you for explaining this - really helpful 😊

Thanks Roger that was a great lecture.

Roger an easy way to check if the coil has gone in a open vented system is to bung your heating expansion tank and then start to run off some water from the heating circuit it will keep running if the coil has split,you will find the domestic tank ball valve starts to drip or run.

Very informative Roger, thank you. I have learnt a lot.

Thanks Roger very educational.

I learned more about how modern boilers work in this video than everything else I have learned over a lot of years! Always love your videos, but this one was outstanding! SO well explained!

That was excellent very informative thank you!

Very comprehensive covering a lot of ground. I have a system which builds pressure but i am waiting for my annual Gas safe service to change the expansion vessel which has a wet schrader and the same clunk sound all round as the system pressure runs up from setting initially at 1.3 bar to level off at 2bar cold and runs at 2.6 so no major fluid losses so far . My boiler is 11 years in service now so my main fears will be upset valves after they have been resting for so long.

Great video. Thank you Roger 👍

Your words of wisdom have been a lot of food for thought and most useful thank you.

Hi Roger, Very impressed! I'm stretching the old memory cells but we had a customer who had a constant overflow dripping issue only to track down that some bathroom company had fitted a mixer tap in a downstairs bathroom sink tap on a vented system with the cold connected to the mains and the hot, obviously, from the boiler. The tap was faulty and mixed.

Thanks Roger. You’re a star. And funnily enough, if I close my eyes and just listen to you, you sound like Anton de Beke!

Warmzilla wouldn't beat my quote of £50

That was a lot more technical than expected. Not a DIY job! It’s great to see this level of non-hand-wavy detail on RU-vid.

excellent work, Thank you.

This is a great video Roger, made for me thank you.

Great video easy to understand

This is beautiful, thank you soo very much

Magnificent presentation !

Brilliant, seen so many alleged heating experts on here that couldn’t explain what you have done in this video.

Thanks for an incredibly useful video. I now realise why, as well as keeping within warrenty, a regular service is important and such as good idea.

Nice clear explanation cheer's

Really nice review, thank you Roger. I'm guessing that a failing or improperly pressurised expansion vessel might lead to a larger difference in dial pressure reading between cold and hot water temp before the system ever goes out of normal green pressure range. For a typical boiler, what should be the difference between cold and hot pressures (how much of the green range would a healthy boiler use)? Also, if that differential is changing, would one pump some air into the expansion tank before the system needed refilling?

very helpful, thank you.

Hi. Well explained. Had preasure system put in 10 years ago, about to have 4th preasure vessel installed - the rubber diaphragms only last a couple of years - wish we had stuck to old fashioned conventional system as only ever cost regular boiler service.

Great explanations.

excellent video. many thanks 👍👍👍👍👍👍

Excellent video thank you

I live in a fairly large 4 bed rented 1970's house with what looks like original rads. The house used to be on an oil fired heating system with immersion heater and a tank in loft etc. In the last 20 years the house was finally connected to mains gas. As part of this the old oil fired heater was removed and old systems decommissioned but old rads left in place. A nice new combi heater was installed, but because this system runs at a higher pressure there was all sorts of leaked and most of the rads had TRV's fitted. This combi heater broke down 3 years after we moved in. A Baxi has been fitted. I'm having to constantly repressurise the system. I haven't found any pipe leaks (I work in property maintenance so I do know a little bit about what to look for). I have reported this to the letting agent and the plumber came and told me that I should report it to Baxi... I'm the tenant it's not my responsibility. I just wish that more "plumbers" watched your vids Roger, they might actually learn something and do a better job. Having watched this vid, when the engineer next comes to do a service I'm going to insist he checks the expansion vessel pressure and the pressure relief valve and for internal boiler leaks.

An Excellent explanation i have learned a lot from this video 💪

Excellent video! I check and charge the vessel on every service of boilers 4+ years old

Really interesting video thanks Roger !

Very good Explanation 👍 👏 👌 😀 ☺

this guy is awesome, thank you. i just fixed my radiator heating issues, the farthest radiator was not heating up and this trick worked amazingly

Hi Roger, I think you just explained why I has a problem in a previous house with a hot water tank with the header always overflowing even though the ball was below water. I changed both ball cocks in the end and it still overflowed. In the end, fiddling with the level the ball valve cut off in highest tank stopped the overflow so left it with that fudge. Luckily the two tanks were close to the same level. You Never mentioned condensate freezing in the external pipe blocking it and causing the boiler to shut down. Apparently, that is very common and my gas-safe engineer says he always gets very busy with those callouts the first time we have a big freeze.

Excellent video Roger... You're a great teacher and explained that in terms that we 'DIY can't afford gas engineers' can now clearly identify where the leak may reside. Thanks.

Thank you for a thorough explanation. Really useful! You covered so much. The plate heat exchanger can also be perforated, leading to a cross contamination of primary and hot-water fluids. Then, depending on which pressure is lower, either the primary pressure drops (rare) or the system keeps getting topped up (not too uncommon). Keep your excellent videos coming.

We had a new Vaillant combi boiler fitted a few years ago which began losing pressure. I couldn't find any leaks at all but eventually had to call an engineer. He came readily armed with a valve so obviously knew the problem beforehand. When I asked why I couldn't find any leaks he said that I wouldn't necessarily notice one because there was a drip tray underneath (very reassuring!) and the heat from the boiler would have evaporated it. Pretty good boiler otherwise but lost pressure yesterday resulting in no heat, so that's why I am watching your video today. Re-pressurised it again and OK at the moment.

Thanks for the knowledge, I found that my system had two 2 port valves with a split heating system operating across 2 zones. I was losing boiler pressure and happened to mention it to a next door as we are on a newish build estate he mentioned that he had to have both replaced. I checked the valves and found a wet carpet in the cupboard which I now plan on changing both of them as might as well if the system is drained looks like to have a weep from inside the valve/motor. Fingers crossed..

Excellent exposition Roger. I wonder how many plumbers know all of the possibilities?

My Ariston combi, now replaced, lost pressure overnight to zero but luckily continued working. Eventually traced to a leaky schrader valve after many years!

Hi, thank you for this video, during the winter I have to refill my radiators once a week every week. So often my family have a system in place to make it quick. During the summer the boiler packs up about 8 times and a quick refill mends that. I have had British Gas around so many times it’s maddening with thermal cameras etc. I have made a note of all the potential problem areas and I will get a plumber round and we can go through them one by one. It can’t be doing my boiler any good. So thank you for this from the bottom of my heart!!!

Our system boiler is in the garage, there is an integral expansion vessel behind the boiler but the schrader valve is way up on the top of the boiler and hard to get to, so I fitted an 18 litre ( way overkill, but we have 14 radiators in the house ) expansion vessel via a tee in the return leg. The pressure gauge is rock solid whether the boiler is hot or cold... I always keep the system well topped up with inhibitor so no chance of corrosion in the expansion vessel. Sometimes the discharge valves can leak water out even though they are not at their discharge pressure.

Just discovered your channel,a little gem, thanks

The expansion tank in the boiler was my issue. After replacement my bills dropped and the pressure in the boiler instead of rising considerably - remained stable. I was topping up the closed system every month or so, and there was a considerable amount of steam during boiler operation - which was the tip I had there was an issue 8n the boiler and nit a leak in the system...

tie a piece of kitchen towel round each of the radiator legs, check them now & then to see if any of them get damp from a leaky joint.

Hi Roger, Thanks for another great video. Another way to check the heat exchanger on a boiler is to disconnect the condensate pipe, put bowl underneath, isolate boiler, pressurise to 2.5 bar leave for a while and then check for water in bowl. Personally I'm not keen on leaving "dead" expansion vessels in a boiler without isolation and fitting an external vessel as over time the vessel will start to leak, so needing another visit to either isolate or replace vessel. Very into fitting slave vessels though, alot of the time needed, but also means boiler will not need topping up between services which is great for people, especially Tenants in rented properties. Going onto heat exchanger failures, we are now testing for concentration of inhibitor (if any) at every service.

Very good explained video

Roger on the Radio... it has a ring to it! Great advice on R2 this week. Guest of the year.

Had a prsure problem would need toping up once or twice a year and told by service guy it was normal till one year, a different engineer noticed the pressure relief valve had been leaking. Replaced it and never had to top it up unless I check radiator bleed valves once a year.

Many thanks Roger.

Cheers Roger, have a great Christmas 👍🏆🇬🇧

Hi Roger great video as usual could you do a video on G3 diagram and regs please many thanks

The flow turbine adapter was leaking on mine for years and I never noticed it. It was a drip every now and then, and until I placed a towel directly underneath and left it overnight did I notice a tiny damp patch, almost imperceptible. I ordered a new adapter, removed the old crusty piece of s**t and replaced it. Now the water pressure is relatively constant and with the expansion pressure back to 1 bar it holds nicely. Those baffles were a real pain in the a$$ to get out being that the flue was directly over it! Mine is a greenstar 28i junior.

Actually the diaphragm runs top to bottom as determined by the seam on the vessel but let's not split hairs.

Thanks so much.......solution number 1 solved my issue

And if the pressure keeps going up, its most likely leaky valves in the (permanently connected) filling loop. Happened to me and my son. Son got a free new plate heat exchanger out of it as service contract engineer insisted it was a pinhole in that despite I told him the disconnected loop had a slow drip, which he said wasn't enough to cause the problem, which he eventually replaced the valve and cured the problem!

Great video on pressure system. 👍👍. I'm always under pressure and leak quite often too. 😉.

Thank you

Why did we get rid of cold water tanks etc? In the event of one's water being cut off you had enough water in the cold water tank to flush the loo if caught short.

Great stuff. Roger

great video Roger 👍

That was super helpful and informative thanks very much 👍🏻

Thank you. Don't know why I didn't see this one earlier when it came out, would have really helped me with my exams. It does explain why my Ariston boiler tried to kill me in 2011 which was when I got interested in plumbing! Leaking heat exchanger. I told Ariston's service engineers there was water dripping very slowly out of the bottom of the combi and it was losing pressure, but they couldn't find anything. The engineer took the face plate off the combustion chamber and lit the boiler. A six foot jet of flame shot out and fried the wiring. He said it was fine. It was a cold February and the boiler was lighting with a huge BANG every time which I now know was forcing gasses out the sides of the faceplate. I phoned Ariston and was assured it was perfectly safe or it wouldn't work. I was falling asleep on the sofa with a massive headache when it suddenly occurred to me to look up Carbon monoxide poisoning symptoms. I was very lucky there. I had weeks of oxygen treatment and the boiler was condemned.

One item not covered and may result in pressure loss is failure of the schrader valve. I was advised to replace the boiler because of daily pressure loss requiring re pressure every day. I got a new boiler fitted and when the old one was stripped out it was found that all that was needed was a new Shrader valve. Like a car tyre sometimes you need a new valve. £1200 down the tubes for a new Baxi Platinum was the result!

Another idea to detect leaks - how about UV dye as used in car air con systems? Obviously no good for leaks under floor where no access but cheaper than expensive ms gas detection.

Good to see your well Roger, been years since I've seen you.. I used to work at Impact Power Tools and Doves in Redhill.. A great presentation as usual..

well done i do like this tips

My boiler was losing pressure and leaking out the bottom. put a bucket under it. Limescale cured the problem after a year or so. F'ing love it when neglect fixes the problem