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Boiler running at 3 bar, is that normal?

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Seasoned Pro
Posts: 1,186
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Registered: ‎28-02-2017

Re: Boiler running at 3 bar, is that normal?

You could always try the old adage....

 

When all else fails read the .... manual!!!

 

Brian

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Anonymous
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Re: Boiler running at 3 bar, is that normal?

@nozzer, there was no air in any radiators, not even the towel rails that are the highest point in the system! But with that said on checking the pressure's dropped to 2.5bar.

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Anonymous
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Re: Boiler running at 3 bar, is that normal?

@bmc Are you actually serious! Wink

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Aspiring Hero
Posts: 2,945
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Registered: ‎05-09-2016

Re: Boiler running at 3 bar, is that normal?

The instructions for my Vaillant combi boiler says that it should run at one bar, and be topped up when the pressure drops below 0.8.  The service engineer usually tops it up to about 1.4 when he's finished, and there is a red line on the gauge at 3 bars.

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Seasoned Pro
Posts: 522
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Registered: ‎19-11-2008

Re: Boiler running at 3 bar, is that normal?

The Worcester bosch advice on sealed system pressure is https://www.worcester-bosch.co.uk/support/troubleshooting/faqs/home-heating-faqs/how-often-should-i-...

 

Last year my boiler system pressure was exceeding 2.5 bar when hot and 1 bar when cold.

I had recently had the boiler serviced and had assumed the service included a check of the pressure vessel...

The pressure vessel is inside the back of the boiler. To replace it would require total removal of the boiler!

 

Taking matters into my own hands:

1) I isolated the feed and return valves on the boiler

2) drained the boiler using its drain valve (not the pressure releif valve)

3) The pressure vessel has a car tyre schrader valve on the air side, I put my foot pump on the valve and inflated the pressure vessel to 0.8 bar. This forced out 4 litres of water from the boiler. Through the open drain valve.

4) close drain valve and open the feed and return valves.

 

Boiler pressure is now 1 bar cold and 1.5 bar when hot 🙂

 

Over time the air had slowly leaked from the pressure vessel reducing the air volume.

 

More info on sealed systems can be found at:

http://wiki.diyfaq.org.uk/index.php/Sealed_system_FAQ#I_suspect_the_expansion_vessel_is_faulty.2C_ho...

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Rising Star
Posts: 263
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Registered: ‎15-10-2016

Re: Boiler running at 3 bar, is that normal?

That time of year again, so....

 

Aim for 1bar when the system is cold. The pressure may rise a bit as the system heats up and the water expands, but the pressure vessel, if working properly, should take care of much of that expansion. The PV has a flexible diaphragm inside it, water on one side, air pressure on the other. If air pressure is lost, or the diaphragm fails, the boiler water pressure in the system can exceed safe limits, where upon the relief valve should open. If that happens (or you have some other water loss from your system) you will find your self constantly having to top up the water pressure. If water appears out of the Schrader valve when the pin is pushed in, the diaphragm has split.

If a boiler has a built in failed PV which is difficult to change, or source a replacement - a quick easy fix, is to install a PV in the system somewhere external to the boiler, leaving the failed one in situ.

Small, slow leaks in the system can be very difficult to find. If all else fails to find the source of a leak, a last resort to trace it might be to drain the system and add air pressure. Air escapes more easily than water and is noisier, making the leak much easier to find. . 

 An easy way to check if a relief valve is passing water, is to fix a plastic food bag over the pipe end with an elastic band. If water appears in the bag, the valve is either passing water or opening under excess pressure.

Some boilers needed a special plastic key to enable them to be topped up - make sure if your boiler is one of those, that you have that essential key to hand.

 

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Anonymous
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Re: Boiler running at 3 bar, is that normal?


@RichardB wrote:

 

I had recently had the boiler serviced and had assumed the service included a check of the pressure vessel...

The pressure vessel is inside the back of the boiler. To replace it would require total removal of the boiler!

 


My pressure kept dropping to zero after topping up to 1 bar.

The Service Engineer confirmed a leaking Pressure Vessel.

 

10 years since installation.

 

Luckily, replacement did not involve dismantling the boiler, just a bit of nifty easing of the PV out.

 

The PV had a split in it.

Replaced, everything is fine now...

 

Expansion vessel (the same thing ?) noted as being changed also

 

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Community Veteran
Posts: 5,658
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Registered: ‎21-03-2011

Re: Boiler running at 3 bar, is that normal?

I had problems with water pressure when I had a loose joint.

Now Zen, but a +Net residue.
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Seasoned Pro
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Registered: ‎19-11-2008

Re: Boiler running at 3 bar, is that normal?


@Anonymous wrote:


 

Luckily, replacement did not involve dismantling the boiler, just a bit of nifty easing of the PV out.

 


 

That seems like good design if the PV can be eased out and replaced.

The recommendation for my boiler is to fit an external PV and hope the failed one in the back of the boiler does not leak 😞

However, as the boiler is an 11 years old Baxi/Potterton condensing boiler it will probably need replacing sooner rather than later 😞

Richard

 

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Hooked
Posts: 6
Registered: ‎24-01-2019

Re: Boiler running at 3 bar, is that normal?

Sorry it's too late as you have probably sorted that problem ou because it is a problem. It is a fault because the system does not have enough expansion capacity or the cold pressure was set too high in the first instance = i.e. above 1 BAR.

It has been found that all systems from cold double in pressure which is attributed to Boil's Law..... Pressure increase remains constant to temperature increase, (in so many words)  If the pressure is at 3 Bar the pressure relief valve (blow off) may well be continually releasing water which requires re-pressurising  on a regular basis which infuses more impurities into what should be a 'sealed' system. For longevity of any system that is sealed that is bad news.

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Hooked
Posts: 6
Registered: ‎24-01-2019

Re: Boiler running at 3 bar, is that normal?

Anonymous ---- You have by now found you are wrong in telling' Richard' he was incorrect.  I see it was you (please correct if I'm wrong) who asked the question in the first instance re 3 bar 'working' pressure. If the fault you most definitely  have is not rectified in time to stop deposits fouling up your system and in particular if your boiler is a low water content one you will have to replace the boiler which will leak. I oncew told a bloke 40 years ago his boiler was noisy which he ignored and within a month that boiler leaked through a cracked section. Your boiler has about 1/100th of the water that boiler had........

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Hooked
Posts: 6
Registered: ‎24-01-2019

Re: Boiler running at 3 bar, is that normal?

Have you noticed the inquirers then say they know more than those who do know what they are at? Those with 3 bar working pressure on low water content boilers  should get ready to replace their boilers if that goes on for long! Especially I find with ali heat exchangers!

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Seasoned Champion
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Registered: ‎21-11-2018

Re: Boiler running at 3 bar, is that normal?

The expansion vessel on the boiler has a bladder inside it that has a normal schrader valve  ( like the one on your car tyres ) on it - the air 'cushion ' can leak out gradually and eventually not be enough air in there to stop the pressure rising and blowing off relief valve.  There is a filling loop ( normally a flexible tube ) connected to normal cold water main allow more water into the system,  this has a shut-off valve and a one way valve to prevent boiler water being forced back into water mains ) this filling loop should have the valve off in normal use anyway so that more water not allowed into system - more modern ones have a spring loaded valve that returns to 'off' position when released,  these have a special removable handle,  the older ones have a screwdriver slot like the service valve on your toilet cistern

The normal temporary cure for system pressure build up and water blown out through expansion valve is to actually drain one of the radiators in an unused room and the air pocket in the radiator will take up the expansion of hot water in the system and help the built in boiler expansion vessel to cope until the problem is sorted.

To top-up the pressure in expansion vessel you will need to de-pressurise the system, just turn off the boiler,  hold the expansion blow-off valve open to dump water until pressure gauge on boiler reads '0' and then locate the schrader valve on expansion vessel ( normally at top rear  of boiler ), attach a normal car tyre pump and make sure the pressure in the expansion vessel is up to spec,  normally 1.1  bar.   now open filling loop to allow water into system until it is up to pressure on the boiler gauge ( just above green normally ) - turn off the filling valve to stop sny more water entering ( otherwise heating system will continue to pressurise until it reaches water mains pressure,  which can be anything up to 4 bar or more ).   I have fitted an external expansion vessel on our system and pressure in system never varies from cold to hot,  ( but our boiler is in garage so plenty of room ).

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Community Veteran
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Registered: ‎06-11-2007

Re: Boiler running at 3 bar, is that normal?

And this thread is 2 years old ! ! ! ...Roll_eyes   Shocked

 

  

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Community Veteran
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Registered: ‎02-08-2007

Re: Boiler running at 3 bar, is that normal?

Time for a new boiler .

These modern boilers have so many bits in them they are just waiting to go wrong unlike the boilers of old that were so simple they could last a lifetime.

Sure modern boilers are more efficient but how much more do they cost to install, service and if they go wrong how much to repair.

Having said that in a few years time no gas boilers will be fitted in newly built houses.