Explanation Please, boiler losing pressure (maybe fixed)

[pinheadplanet]

Hi

Halstead Ace High (Combi) was losing pressure and the PRV was being activated every time I refilled it (to 1.3bar-cold). PRV is a 3.0bar PRV but pressure only ever went up to about 2.6bar, so it would seem it was being activated early.

I checked the pressure in the expansion vessel and it's 0.7 bar which is about right (no water came out either).

I removed the PRV and gave it a bit of a clean with a brush and some DS-3 I had lying around. Replaced everything and repressured the water back up to about 1.1bar.

Now the PRV doesn't seem to get activated and the pressure is sticking to around 1.1bar when cold (only been a day since I done it all) BUT the pressure when the heating is on only goes up to about 1.6bar. It has never gone up so little when the heating has been on, normally above 2bar, IS THIS OK? And why would that happen, does it make sense?

Thanks

Kelv

 

[John506]

0.7 bar on the expansion vessel?

Does it say that in the MI or on the expansion vessel itself?

Just seems a bit low.

 

[pinheadplanet]

I took the reading with a pressure gauge from the expansion vessel.

According to the boiler manual the exp vessel should be about 0.3 bar below the recommend boiler pressure when cold, so I think that's about right isn't it?

 

[arfurrrr]

how did you take pressure reading ? with or without system open

 

[pinheadplanet]

Not sure what that means. The system was pressured up but cold.

 

[Mikefromlondon]

As you had asked for explanation, this is general and not specific to your boiler, i had a Vaillant combi, which needed frequent filling and almost to a point it required daily filling, the expansion vessle nipple squirted water out instead of compressed air! so I knew my Expansion Vessel had a leaky diaphgram, the remedy would have been to remove the boiler from the wall, and replace the leaky vessle with a new one , this was going to be a lot of work, so instead I bought a 2nd hand vessel from a scarp dealer locally, that actually came from a similar boiler and fits mine exactly, I tested that it had air in it so I knew it was in good order.

I plumbed it into the return circuit very close to my boiler, and presurised it to 1 bar and since this I haven't needed to fill even a drop of water! and the water has not leaked and the pressure only ever climbs up by about 1/4bar or will rise slightly higher depending on the CH flow temperature setting.

Any way, some pressure rise will happen as the exapnsion vessle has compressed air in it, so for water that has been heated and expanded will force its way inside this expansion chamber, and it therefore must oppose the compressed air, which in doing so will result in overall pressure increasing in the CH circuit, as well as in the compressed air chamber, which depends on the temperature of the flow, higher the flow temp and higher the pressure increase, on cooling the pressure returns to normal 1 bar as reccomended for that boiler.

PRV are prone to dripping if activated manually, any debri in the system can settle in the valve seat and cause it to drip and you could still loose water slowly. I had one where I had to test it for correct function, and once I activated it, it would not stop dripping! where I had to remove it to clean its seat and refitted it back.

 

[swbjackson]

Not sure what that means. The system was pressured up but cold.

The expansion vessel pressure should be checked with no pressure in the boiler. The normal way of doing this is to isolate the boiler from the system and open a drain off on the boiler. If you check the pressure with the system full you will just get a reading of the system pressure.

 

[pinheadplanet]

As you had asked for explanation

Hi Mikefromlondon, if your pressure only raises by about 1/4bar then that's about the same as mine now. My expansion vessel is sound as it doesn't have water coming out from it. I still don't understand how it could have been so different before though, all I've done is remove the PRV, clean it and put it back.

swbjackson: Yeah I had drained all the water from the system, so no water pressure. That's the right way to measure it isn't it? (I was wrong when I said the system was pressured up before - the old ME kicking in I'm afraid)

 

[Agile]

You usually air pressurise to about 0.9 Bar and water pressurise to 1.0 to 1.5 bad.

Then the hot pressure will increase by about 0.3 Bar when the system is hot.

Tony

 

[pinheadplanet]

You usually air pressurise to about 0.9 Bar and water pressurise to 1.0 to 1.5 bad.

Then the hot pressure will increase by about 0.3 Bar when the system is hot.

Tony

Cheers Tony, any idea why it was going right up to 2.6 bar prior to me cleaning out the PRV?