Boiler pressure gradually increasing?

[Juswundrin]

Hi

The pressure gauge on the expansion vessel of our (oil) boiler is creeping up bit by bit.

When hot, it's been showing 1.5, 1.6 the next day, etc and is now just above 2.0; cold, it's gradually increased from the usual 1.0 until its current 1.3ish.

I believe this usually means that the diaphragm in the expansion vessel has split, is that right?

The overflow from the expansion vessel is shared with the overflow from the chauffe-eau; this overflow froze a couple of weeks ago during the cold weather, so it occurred to me that the water which drips from the chauffe-eau, unable to exit from the overflow, could have ended up inside the expansion vessel, does that sound possible?

Anyway, short question; is there something simple I can do to rectify this, or is it a job for the plumber?

Thanks

[jondeau]

The answer to your questions is...........No and No......as to the third, it's not a difficult job.

It sounds most likely that the stopcock that supplies water to top up the heating system is faulty......it may just need a new tap washer in it.

Unfortunately many French heating systems only have one isolating valve between the heating system and the mains (in the UK it is always two valves) and this means that you would have to drain the heating system as well as shut off the mains to change the tap washer.

 

[Le Plombier]

My money would be on a perforated diaphragm in the expansion tank

Provided it has been installed with the correct union, they are normally supplied as part of the equipment, you simply need to unscrew the union nut and fit a new one

If correctly fitted there is an isolating plug in the union on the tank connection, this closes as the tank is removed and reopens as the new tank is connected

If you have any doubt then drain down first

If the diaphragm is perforated be careful as you will not believe the weight of the expansion tank, once you remove it you will know immediately, from the weight if that is your problem. the reason why it is so heavy is that it is full of water

If it was a defective fill valve on the cold water supply side then the pressure would keep on rising regardless of the system being hot or cold until it reached mains water pressure or the safety valve discharged( 3bar)

On the point raised by Jondeau it is law here in France that twin isolating valves are fitted on the make up supply, in between the two valves a air break valve must also be fitted to prevent contamination back in to the water main

A lot of gas boilers come with the assembly prefitted, all other boilers should have this equipment fitted by the plumber, most don't as it is more expensive

Le Plombier

[jondeau]

[quote user="Le Plombier"]

 

If it was a defective fill valve on the cold water supply side then the pressure would keep on rising regardless of the system being hot or cold until it reached mains water pressure or the safety valve discharged( 3bar)

On the point raised by Jondeau it is law here in France that twin isolating valves are fitted on the make up supply, in between the two valves a air break valve must also be fitted to prevent contamination back in to the water main

[/quote]

 

 

I do believe LP, that the poster did say that the pressure kept rising when the system was cold......

Quote.  'cold, it's gradually increased from the usual 1.0 until it's current 1.3ish

Therefore I'll stick with my original diagnosis first.

 

 

It may well be the law in France LP.......and I will admit that I have only ever seen older systems.......but believe me it is rarely (if ever) adhered to on those.

regards JD

 

[Juswundrin]

"I do believe LP, that the poster did say that the pressure kept rising when the system was cold......"

Sorry, I wasn't clear; when cold the pressure was static, but each time the system cooled down the cold pressure was slightly higher than the previous time. Reading that back, I'm not sure it's much clearer now...

Anyway, thanks to both of you for the help. I thought I'd wait to reply until I could confirm what the problem actually was; the plumber has just fixed it, and it was indeed the diaphragm which had failed.

Thanks again.

[jondeau]

Thanks juswunderin, it is nice to get a bit of feedback...........

Cheers, jd.

[Le Plombier]

If it had been the fill valve letting by the pressure would have risen constantly to the extent that the system safety valve would have been discharging all the time

99% of the time when it is this type of problem it is invaribly the expansion tank diaphragm 

Le Plombier

[jondeau]

Well yes, it would.......assuming of course you had a mains pressure of 3 bar or above.

In the area I live in (South Devon) it's a good day if the mains pressure reaches 1.6 bar, I have no reason to believe the situation is any different in France. On top of that of course, many houses have pressure reducing valves fitted.

As you know, the only way a system pressure can rise when it is cold is by the introduction of more water to it, given the French penchant for fitting a single stop valve between the heating system and the mains then the most logical thing is to check that before moving on to other components and spending money unnecessarily.

Not of course that this is a big problem generally, I was thinking back today....and can only recall two occasions of having to change an expansion vessel in fifty years......

 

 

Meanwhile........the joys of the plumbing /heating business.....I went to a friends holiday cottage yesterday, it had been empty for a few weeks, the place was freezing and he had a burst pipe, just before the tap connector at the back of the bowl on a kitchen sink. There was an inch or so of water and grunge all over the kitchen floor for a plumber to lie in as he tried to get at the pipework.......

I turned off the mains and organised somebody to come and repair it.......Ah the joys of being retired from the plumbing/heating business.

[Le Plombier]

Jondeau

The typical mains pressure in rural areas of france is 5/6 bar and can rise above this overnight when there is no demand for water

Most properties have a pressure reducing valve fitted to reduce pressure to 3 bar

Believe me, I live and work in France as a plumber and heating engineer, if there is a problem with the heating fill valve letting by the safety valve will be constantly discharging

Expansion vessels fail frequently out here

A lot of things are very different in France compared to the UK

Le Plombier

[BIG MAC]

I am with both posters on this it's simple enough to unscew the expansion vessel and it will soon be apparent if it has any water in it. Switch the water off at the mains as well as the appliance isolation and open an out let to take pressure off.

I note that the overflow froze this means it was discharging possibly due to creep on the isolation valve this would leave the mains pressure nowhere to creepto and it would find the next weakest link ie. the expansion diaphragm.

I would advocate a scheme of works including the double isolation with air gap and a new expansion vessel making sure that the system is charged with fernox or similar water conditioner.