# Gas Boiler has no pressure



## Mahons

Hi, 

Overnight our boiler has lost all pressure therefore not firing. We do have a supply in to the house as the hob is lighting ok. I bled the system last night as it's the first time we've turned on the system since last spring. Could that have anyhting to do with it. 

Regards,

Mahons


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## BillK

Do you mean there is no water pressure? If you have a combination boiler the water pressure should, ideally be about 1 bar for the boiler to work effectively. If this is the case then you need to top up the system. If you don't know how to do this then you need to get the boiler looked at by a professional; if the lack of pressure is on the gas side, then you need to get the boiler looked at by a professional.

It is no job for an amateur as mistakes on your part could be lethal!


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## nai

if it's a new house you probably have a valve for re-pressuring the system from the mains just under the boiler with - prob just has a screw to turn (not handle) just turn it and watch the pressure guage climb until about 1.5 bar (do this when cold!)


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## Mahons

From what your saying BillK it sounds like the water level is low, what could have caused this over night

Not really sure how to refilll it so best to get someone int to look at it. Thanks for your help

Mahons


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## mich

i had a similar problem last year. it was due to a blown circuit board. Hope thats not the answer as it was pricey to fix


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## Mahons

hopefully not, the system is only 10 months old

Mahons


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## Mahons

nai you're a genius, eventually found the valve in the hotpress and straight away the pressure went up and the boiler kicked in.

The wife says thanks!

Any idea why the pressure would disappear like that...


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## dillons

Used to happen to me in my last place during the winter. Had Bord Gais engineer out & he said it was just one of those things that can happen in cold weather with freezing... I never really believed it but learnt how to fix it.

I've since moved & had to bleed the rads... that caused a drop in pressure to zero so I had to turn the tap in the hotpress until it rose to 1.


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## fobs

I have the exact same problem so going to try out your solution this evening!


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## col

I had the same problem last year and I had to top up several times before the pressure stableized at 1.5 bar. This year I only had to top it once after the summer shutdown.


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## 3ps

I have the same and always suspected it was due to a small leak.


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## Carpenter

I've always been puzzled myself about the pressure drop and inquiries with a heating installer yielded nothing more than "it's just one of those things".  I imagine some water is lost from a system over time through evaporation and some of the plastics used in plumbing installations are not 100% vapour proof, leading to losses over time.  Every joint, union and valve is a potential exit point for minute quantities of water also, especially through less than effective gland seals and the like.  I think it's normal to expect to have to top up a system once or twice in a year, especially after a system has been shut down for some time.


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## dillons

I agree carpenter but my experience last year in the apt I then owned was around 3 times a week during any cold spells!!
the Bord Gais appointed service engineer couldn't find anything wrong or any leaks & put it down to cold weather & 'one of those things'!


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## fobs

> if it's a new house you probably have a valve for re-pressuring the system from the mains just under the boiler with - prob just has a screw to turn (not handle) just turn it and watch the pressure guage climb until about 1.5 bar (do this when cold!)


 
Worked a treat!

Our boiler was working agian last night after letting more water into the system. It was most likely due to bleeding all the radiators a few evenigs before but worked a treat so thanks for advice.


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## Holy Well

I turned the valve on my Boiler last night, and it went from 0.2 to 1.5, but within about 2 hours it went back down to 1. 

It remained at 1 overnight. 

Any suggestions?


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## Welfarite

From a previous post above, 1 bar  sounds about right.


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## marty004

Hi,
Just noticing this post.  Our boiler has a label on it saying that normal pressure should be between 1 and 2.
It also says that if below 0.3 you should contact someone.
Ours constantly remains at 0.4 ->0.5 and has NEVER been at normal pressure since we moved into the new house (2 years ago).  We only noticed this when it started making strange squeeling noises and having problems with our water pressure so we immediately got someone out to look at it.
We were told it was fine.
It doesn't seem fine to me when you hear the noise and you're having a shower and the water stops coming out.  
Is the boiler guy correct in saying it is ok and if so why if the pressure isn't in the normal range?  Or should I get someone else out to fix the pressure?


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## slan98

Hi 

Having same problem in new apt with boiler, pressure is at 0, can anyone let me know exactly where this valve is or what it looks like....ta!


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## gianni

Our valve is in the hot press on one of the pipes leading into the water tank. It is a small black 'tap' that looks more like a switch than a tap. It doesn't turn in a circle but rather 90 degrees to open and 90 degrees to close. Dunno if our setup is common or not so I'd advise caution before fiddling with taps/valves in your hotpress!


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## pat127

Does anyone know what a 'semi-sealed' system is? That's what I was told  I have since I switched to gas.The tap in the hot-press is permanently open and the pressure remains steady at 1 bar. I've had absolutely no problems except to bleed the system - the first rad in particular - every few months.


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## davidoco

pat127 said:


> The tap in the hot-press is permanently open and the pressure remains steady at 1 bar. I've had absolutely no problems except to bleed the system -



The reason it remains at 1 bar (it must change between heating off and on) is that there is a non return valve before that valve which stops water from your heating system going backwards into the public supply so your pressure will stay at whatever the supply to the house is and in Ireland that is usually not more than 1 bar.  You really should close the inlet valve and see how things go.

Good place to help identify fittings

http://www.sanbrafyffe.ie/products.html or www.rwc.co.uk

bottom of this page to see non-return valve which is usually brass [broken link removed]


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## davidoco

gianni said:


> Our valve is in the hot press on one of the pipes leading into the water tank.



That valve is either the cold water feed to the tank which enters at the very bottom 

or more likely the return of the heating coil in the cylinder which is about 3/4 way down.  Its purpose is to balance the system.  You either get loads of hot water before your rads heat or you have a bit of both.  

Sometimes an air lock can develop there and opening it fully for a bit moves the air along.  You should really return it to its original position (not fully closed!) to return the system to the balance that the installer set - unless of course he didn't bother to get it set right in the first place.  That valve on most installations is a wheel valve which people tend not to mess with.


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## pat127

davidoco said:


> The reason it remains at 1 bar (it must change between heating off and on) is that there is a non return valve before that valve which stops water from your heating system going backwards into the public supply so your pressure will stay at whatever the supply to the house is and in Ireland that is usually not more than 1 bar. You really should close the inlet valve and see how things go.
> 
> Good place to help identify fittings
> 
> http://www.sanbrafyffe.ie/products.html or www.rwc.co.uk
> 
> bottom of this page to see non-return valve which is usually brass [broken link removed]


 
Great, thanks. The pressure falls to just over 0.5 bar when the system is off. What should happen when the valve is closed and are there any negative aspects to watch for?


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## davidoco

pat127 said:


> What should happen when the valve is closed and are there any negative aspects to watch for?



The water inlet valve that we're talking about should be shut unless you have to refill or top up the water.

Remember every time you find air in a rad and bleed it the pressure will drop.  An idea might be to open that valve some saturday morning early when heating is off and bring the gauge up to 1.  The reason for Saturday morning early is that is when you see better water pressure as there are less businesses and people using water and you might get some extra pressure at the tap to force water into the system.

Heating systems with the water inlet valve, non return valve and small red cylinder should ideally be free of air and full with water at 1 bar when cold.  Heating when on will then push that to between 1 and 2 bar - depends on how hot your boiler is running. If you have to bleed a rad because it is cold at the top you will need to go back to the valve and let in a bit more water to bring the gauge back up to 1 bar when cold.

Ideally once you have filled to 1 bar you should not have to top it up more than once or twice a year. If you find that you do have to keep topping up there must be a leak somewhere.  When plumbers say "it just happens that the pressure drops" this is because plastic pipe work allows air out of the system very slowly and that causes a pressure drop and not a leak of water, but that should be only noticable once a year.

Another word to complicate issues, most sealed systems will have a small "bottle"  air vent fitted at the highest part of the system on top of a piece of 1/2 copper.  see [broken link removed]  This device will try and trap and release any air in the sytem that reaches it.  So by and by during the year it is capturing air that has been hiding in the system and releases it thereby reducing the pressure in the system that needs to be topped up.  Remember water contains oxygen (air) and the heating process in the boiler can seperate this air from the water but it does this relatively slowly and only if your boiler is set relatively high.


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## collieb

marty004 said:


> Hi,
> Just noticing this post. Our boiler has a label on it saying that normal pressure should be between 1 and 2.
> It also says that if below 0.3 you should contact someone.
> Ours constantly remains at 0.4 ->0.5 and has NEVER been at normal pressure since we moved into the new house (2 years ago). We only noticed this when it started making strange squeeling noises and having problems with our water pressure so we immediately got someone out to look at it.
> We were told it was fine.
> It doesn't seem fine to me when you hear the noise and you're having a shower and the water stops coming out.
> Is the boiler guy correct in saying it is ok and if so why if the pressure isn't in the normal range? Or should I get someone else out to fix the pressure?


 
Marty,

A lack of pressure in your heating system shouldn't have any affect on the amount of water coming out of your shower - they are 2 separate systems, and that sounds more like an air lock in the domestic water supply. If pressure is low on your boiler guage, do as advised already here on this post, open the valve in your hot press and let some water in when system is cold until pressure builds to 1 bar, then close the valve and watch what happens when the heating kicks in.


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## davidoco

marty004 said:


> We only noticed this when it started making strange squeeling noises and having problems with our water pressure so we immediately got someone out to look at it.
> We were told it was fine.



Marty you mentioned somewhere else that you had a combi boiler but you also had a large tank in the attic.  You have a pump somewhere (usually on top or beside the attic tank) that generates the pressure for the incoming water to the combi which in turn feeds your shower with hot water.  Your electric shower is also fed cold water from this pump and I bet it's a Mira Sport or similar.

The next time you run out of hot water in your hot water shower and hear the pump go up to the attic and see if there is any water in the large tank.  You may be running it dry, ie incoming water from the mains can't keep up with the pump.  You will need to adjust the pump down a bit or else your pressure reducing valve needs adjusting or is acting up - two jobs that might be best left to a plumber. 


collieb also has a good point that your combi boiler is at the incorrect bar.  It may be unable to heat the shower water effectively thereby causing your thermostatic valve to lock in at the shower. Another reason to make sure you get your bars right on the combi.


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## pat127

davidoco said:


> Another word to complicate issues, most sealed systems will have a small "bottle" air vent fitted at the highest part of the system on top of a piece of 1/2 copper. see [broken link removed] This device will try and trap and release any air in the sytem that reaches it. So by and by during the year it is capturing air that has been hiding in the system and releases it thereby reducing the pressure in the system that needs to be topped up. Remember water contains oxygen (air) and the heating process in the boiler can seperate this air from the water but it does this relatively slowly and only if your boiler is set relatively high.


 
That's extremely comprehensive, thanks for all the tips. I've located the non-return valve and also the bottle air vent. There are 2 more vents above the boiler also. Is it okay to leave all these vents slightly open?


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## davidoco

pat127 said:


> There are 2 more vents above the boiler also. Is it okay to leave all these vents slightly open?



I'm not sure what these two vents would be.  One is likely to be the pressure relief valve which is piped to the outside like a drain pipe.  It is r shaped usually with a black knob on top.  

I see in your first post that you said semi-sealed and I've never heard of that.  What might have been said to you that your heating circuit is sealed but your hot water is vented to your attic tank therefore giving your a "semi sealed system".  Most new instllations now are fully sealed pressurised hot water and central heating.


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## pat127

davidoco said:


> I'm not sure what these two vents would be. One is likely to be the pressure relief valve which is piped to the outside like a drain pipe. It is r shaped usually with a black knob on top.


 
That's there as well. I'll ask the service-man about the other 2 when he comes in March.



davidco said:


> I see in your first post that you said semi-sealed and I've never heard of that. What might have been said to you that your heating circuit is sealed but your hot water is vented to your attic tank therefore giving your a "semi sealed system".


 
I'm sure you are right as the house is over 30 years old. I obviously misunderstood what I was told.

Many thanks again.


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## marty004

Cheers fellas for all your help.
They have been again a few times now and have decided that the tank in the attic needs replaced.
We are still having the water problems.
In fact our electric shower no longer works at all even when our other showers are working.  They think it might be an air lock.
They also mentioned about "dirt" being in the combi boiler which is effecting the pressure gauge.
I just wish they get it sorted.
It's a bit embarrasing having guests come to your new house and teh shower cutting out on them after 2minutes!!
Anyway, thanks again.
I'll print this off and see if they have tried any of these things.
Don't want to tell them how to do their job though, but it is getting ridiculous at this stage.


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## Manchesterbu

fobs said:


> Worked a treat!
> 
> Our boiler was working agian last night after letting more water into the system. It was most likely due to bleeding all the radiators a few evenigs before but worked a treat so thanks for advice.




My girlfriend & I just returned from holiday & had no hot water!
I'm an utter dunce when it comes to things like this.
It's a rented flat with a Potterton performa 28 boiler
I had to pull out a wooden panel to get at the tap but once I twisted it the pressure gauge bounced up & the problems solved!

Thanks guys!!!


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## col

Had a similar problem on my boiler with pressure dropping below 1 every night. I had to top up the water every day to get the boiler to work. I assumed I had a leak and had a plumber out to look at it. He took out an air pump (foot bicycle pump) and pressurized a chamber in the system to give a type of back pressure. No leaks , no faulty parts just air was required. System has worked perfectly ever since and stays above 1.


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