# Gas boiler losing pressure



## peteb (29 Jan 2014)

I have my gas boiler regularly serviced.  But for years the pressure regularly drops within the system so the boiler can't come on when it's timed to.  

Usually its liveable with, but yesterday it went 3 times in the course of the day.  Gas boilers and water systems arent my forte.  All I do to fix the problem is go to the hot press, turn the little black tap and allow more water in.  

We had a plumber out servicing the boiler and he had said there was no visible signs of a leak in the house so it was probably underground somewhere.

I'm more concerned going forward that I will get hammered on water charges if the leak is on my part.  

Any one any insight into these problems and a solution? Cost-effective solution I may add as we are one-income with a baby so money is hard to find.


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## Leo (29 Jan 2014)

peteb said:


> I'm more concerned going forward that I will get hammered on water charges if the leak is on my part.



As it's leaking from within the heating system, it is under your control.

There's an added problem here in that every time you top up the system you are diluting the level of corrosion inhibitor in the system.


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## peteb (29 Jan 2014)

Ok but how do I go about sorting? Am I going to have to bring in a fella with a thermal imager and dig up my floor? (usual celtic tiger house - thrown up in 2005)


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## Shane007 (29 Jan 2014)

First of all, there should be a small copper pipe exiting from the boiler through the external wall to outside. Is there any signs of wet coming from this pipe, even small amounts, especially when the boiler is on?


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## Seagull (30 Jan 2014)

We had a similar issue a few years back, and it was because the expansion vessel had perished. As the system came up to temperature and the pressure increased, there was no give in the expansion vessel, and so water was being forced out the overflow pipe. 

I'd expect a plumber to check that given the symptoms you've described. Did he make any mention of the pressure vessel?


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## col (30 Jan 2014)

Like Seagull I had a similar issue with pressure constantly dropping and thought I had a leak. I got someone who services gas boilers and it turned out I had no leak. All he did was pressurise a vessel in the hot press where the hot water is stored by pumping it with air. No parts required just air. Cost about €60 for his time.


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## brian.m (14 Feb 2014)

Hi Pete,
Basically if you are loosing pressure there are a few possible causes ,

1 - leak in pipe work - easy to spot if it's upstairs as your downstairs ceilings will be wet .. If it is leaking downstairs beneath the concrete slab of your floors it's not so easy to find . There are leak sealers available and these do work
Depending on the leak rate.

2 - expansion vessel diaphragm has ruptured - you may have an expansion vessel in your boiler or an external vessel on your heating system. If you have an external vessel you will notice a valve (schrader valve) , it's similar to the valve on your car tyre - press in the valve stem and air should come out - if water comes out your expansion vessel is knackered .

3 - your boiler heat exchanger could have a leak - if it is a condensing boiler then you have a drain for condensate - the leak could be going to drain .

If you can let me know what type of boiler (make and model) you have I can provide more info .

Hope this info is of assistance to you 

I am a registered gas installer .. Here to help 

Regards

Brian


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## Shane007 (14 Feb 2014)

It could equally be just no air in the vessel & just needs re-charging.


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## Brendan Burgess (17 Nov 2016)

I have the same problem.  No sign of a leak anywhere. 

I was due a service anyway, so the guy came out and serviced the boiler. Then he turned a black valve in the hot press for only about a minute until the pressure came back up. 

It worked fine for the past 10 days, but I wasn't using it that much. 

Is it ok for me to turn the black tap until I see the pressure coming back up in the boiler?  This is probably only a temporary measure, as I presume that the pressure will drop again in the next few days and I need to get him out again. 

Brendan


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## peteb (17 Nov 2016)

happens to me regularly.  happened this morning. you can top it up but supposedly you shoudlnt have to! and isnt good.


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## Brendan Burgess (17 Nov 2016)

Thanks

But how do I know how long to turn the black tap for? 

Brendan


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## pudds (17 Nov 2016)

Brendan Burgess said:


> Thanks
> 
> But how do I know how long to turn the black tap for?
> 
> Brendan



Brendan the boiler should only be topped up to 1 or 1.5 bar, but max 2 bar. I would stick with
the lower pressure of 1 bar especially if you are topping up a lot.

I have a pressure gauge on the filling loop in the hot press and this is a godsend for knowing how
much to top up the boiler. It will give you a good guide how much to topup by, you will see  or get to know that if you top up HP gauge to say 1/4 or ten to the hour etc that this will give you roughly the pressure or bar that you want on the boiler and you can set the red marker arrow on the
HP gauge to mark this for next time. Hope I'm explaining this ok. 

€100 job including a gauge, my guess, well worth having.

There is some natural evaporation in all systems, so topups are necessary but if you have to top up
a lot I would suspect a leak in the  system.  Over the heating season I would top up maybe 3 or 4 times but I would never let the the water drop to the red zone on the boiler gauge.

If you keep topping up even though you expect a leak, the harm that can be caused is that the inhibitor (if any) in the system is getting diluted and that may reduce your protection against corrossion.

Disclaimer: I am no Expert, just my 2 cents worth.


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## Shane007 (17 Nov 2016)

You should have a gauge beside the fill point.
Topping up the system should really be only done when the system is cold and this is when a true reading will be obtained. Doing it when the system will only be when the water is expanded due to being hot and give a higher pressure reading.
Typical two storey houses should have a cold pressure reading of between 1.3 to 1.5 bar pressure.
Water does not evaporate from sealed systems.
What is often mistaken with small drops in pressure over a given time period is expansion vessel schrader valves. These are the same valves in your car tyres and similarly you have to top up the air in your tyres regularly, air leaks out of the schrader valve.
An expansion vessel has a rubber diaphragm in it and on one side of this is a wet side (the heating system side) and an air side.
Heating system having 1.3 bar and air side 1.0 bar. 
Air leaks from the schrader valve lowering that side of pressure, thus the wet side expands more into this, slightly lowering the wet side pressure.
The air side must be topped up annually, usually carried out during the boiler annual service.
If neglected, it can emulate a leak in the system and lead to total lack of system expansion. Water from the system can then be lost from the boiler pressure relief valve.


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## Brendan Burgess (18 Nov 2016)

Guys - I don't understand any of that. (I have no idea what a "bar" is or how I measure it. If I can measure it with my current set up, tell me how.)

Could one of you give me a Noddy, Step by Step, Guide to what I need to do to get the heat back. If I should not attempt it myself, let me know and I will get someone to do it.

Current situation:
When I turn on the heat, it does not come on.
When I look at my Veissman boiler, there is a message F5 and the reset button is flashing.
I have now switched off the heat and pressed the reset button.

Can you tell me in clear steps, something like the following (The order may be all wrong.)

1) Go to the red tap in the hot press and turn it  fully on  on for 2 minutes
2) Turn off the red tap fully.
3) Turn on the heat at the switch inside the house
4) At the boiler - if the reset button is flashing, press and hold until it stops flashing. 
5) If that does not work, repeat the process ...

Thanks


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## pudds (18 Nov 2016)

I googled that F5 error your getting Brendan and apparently its not a diy job as 
 it involves opening the combustion chamber. You should call a registered boiler engineer or if its under guarantee call the agents.


http://www.diynot.com/diy/threads/fault-code-f5-on-viessman-vitodens-100.251475/


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## dub_nerd (19 Nov 2016)

Shane007 said:


> An expansion vessel has a rubber diaphragm in it and on one side of this is a wet side (the heating system side) and an air side.
> Heating system having 1.3 bar and air side 1.0 bar.
> Air leaks from the schrader valve lowering that side of pressure, thus the wet side expands more into this, slightly lowering the wet side pressure.
> The air side must be topped up annually, usually carried out during the boiler annual service.
> If neglected, it can emulate a leak in the system and lead to total lack of system expansion. Water from the system can then be lost from the boiler pressure relief valve.



This is the first time I've heard something that could be like my problem. Have never had a heating season since the house was built when something didn't break down. I've gotten used to sorting some problems out myself. Boiler (oil burner) constantly leaks water from a pressure release tap on the side of it. It's a good thing it's in an outhouse and I can put an old paint bucket under it. After a couple of days of operation it'll have leaked a couple of gallons. Eventually there won't be enough water in the system and the boiler cuts out. I top it up again using a tap in the hot press, which has its own pressure gauge. Unfortunately that tap seems to have a problem too, since even if it it left closed for a couple of months in the warm season the pressure seems to rise to about 3.5 bar. But I don't know if I trust the reading, because it often stays stuck at that reading even when the boiler clearly has no water in it.

Anyway, even if the pressure is too high, my question is why the pressure relief tap on the boiler doesn't just leak until it reaches normal operating pressure, and then continue to function. Could it be the expansion vessel problem that you mentioned? I'm not aware of the boiler service guy ever doing anything to the expansion vessel. Suppose I test it myself and there is no air? How do I "reinflate" it?


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## Brendan Burgess (19 Nov 2016)

I had a guy out yesterday and the pump is gone.  

Brendan


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## dub_nerd (19 Nov 2016)

Found this great online article about testing and adjusting an expansion vessel. It's from the US but I would guess mostly applicable to here (apart from pressure in PSI instead of bar):


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## Brendan Burgess (21 Nov 2016)

While I am getting the pump replaced (€260) , they have recommended a Power Flush (€650) and a magnetic filter (€300)

From reading this great post by Shane 007, I understand what a Power Flush is. 

However, as the system is 6 years old, I presume I will be replacing the boiler in the next year or two, so spending €950 now does not seem to be cost effective. 

Brendan


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## dub_nerd (21 Nov 2016)

My plumber mentioned magnetic filters to me before. Iron oxide gunk circulating in your pipes sticks to it and can be removed. Apart from suggesting it was effective, he didn't say whether it was necessary or mention a price. Like you, I'm inclined to wait until my old rust bucket of a boiler finally gives up the ghost. On the other hand, this was on the occasion of him having to replace a pump that was full of brown sludge. I don't like the thought that it might also be accumulating in my underfloor heating.

EDIT: after reading your link to Shane007 I realise my plumber might have been talking about the "MagnaCleanse" which sounds like it is used during the flushing process but not installed permanently.


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## newirishman (21 Nov 2016)

Brendan Burgess said:


> While I am getting the pump replaced (€260) , they have recommended a Power Flush (€650) and a magnetic filter (€300)
> 
> From reading this great post by Shane 007, I understand what a Power Flush is.
> 
> ...



I would expect a Gas boiler to last way longer than 8 years. more like double that - at a minimum. That is assuming it is serviced regularly.


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## Brendan Burgess (21 Nov 2016)

I would have expected longer than 6 years - I would not have expected 16 years though. 

Technology changes. For example,  new boilers has a flow valve instead of a pressure valve, so they don't cut out when pressure drops. 

I get a 5 year warranty with the new boiler.  and they install the magnetic filter which seems to make the whole system more efficient. 

Brendan


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## JohnJay (21 Nov 2016)

Brendan Burgess said:


> I would have expected longer than 6 years - I would not have expected 16 years though.



My boiler is 20+ years and still going strong. Hopefully it will keep going for a few more weeks until I sell the house!


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