Boiler pressure driving me mad

jambo9421

Had a boiler stove and new ariston eco boiler fitted around 2014..pressure would only ever be around 0.2 bar because it was a open system..it never gave us the performance we expected..got a power flush done in Oct 2021 and plumber recommended to get the stove disconnected and make it a sealed system..we got that done,he fitted a expansion vessel in the loft and pressurised it to 1.2 bar..had a few issuses pressure was always increasing but that was due to a faulty fill loop valve..now it doesn't hold pressure its dropping pressure from 1.2 bar and staying around 0.4 bar in around a day..no signs of any visible leaks..nothing from the relief valve..I've a small drip under the boiler from a water tap but It's a very small drip..I would appreciate any ideas pls

John.G

Assume EV (expansion vessel) in attic with boiler on ground floor and using the boiler pressure gauge for filling?. its possible that plumber set the precharge (air end) pressure and the filling pressure the same which means no water reserve in the EV so pressure will fall very rapidly to the static head from the rad tops down to the boiler if the PG is on the boiler.

You only have to drop the level a small bit so no water at the EV, check the pre charge pressure with a tyre pressure gauge or whatever, set/reduce this pressure to 0.7bar and then fill the system to 1.5bar, this will mean that you have a (cold) water pressure at the EV of about 1.0bar so this, with that precharge pressure of 0.7bar will give a litre or so of water reserve. If no leaks after restoring filling pressure to 1.5bar after venting then should not require top up for many months.

Paul_Mc1988

https://www.boards.ie/discussion/comment/118414477#Comment_118414477

I have a pressure gauge at the expansion vessel and the boiler. Boiler reads 1.6 bar always but EV one is dropping off slowly over a few weeks. I'm gonna try this

John.G

Normally, the EV (water side) pressure will read, boiler pressure minus the elevation, that is the distance between the EV and boiler, if the EV is located say 5M above the boiler then it should read 1.6-0.5, 1.1bar

10-10-20

Sorry for butting in - I didn't want to open a new topic on this as it seems to be a simple question. I've googled this for a while without getting anywhere!

I fitted an EV in my hotpress (on the recommendation of the boiler service engineer) as I could not get a plumber in November and I was draining down for other radiator work anyway.

My heating system is closed, but the backfill is performed in the same hotpress via a one-way-valve and isolating valve from the attic cold-water tank. For that reason my boiler shows ~0.2 bar when cold, rising to ~0.8bar when hot. I also fitted a pressure-gauge in the hot-press on the feed to the EV and it corresponds to the boiler (minus a small amount due to the height of approx 4 meters difference).

The EV came with 1.6bar of pressure on it, which I considered was too high, so I dropped it to 1.1bar. But going off your guidance, I should lower it further. Should I take the boiler cold pressure or the hot pressure and then subtract the height? ie: 0.8 - 0.4 = 0.4bar?

Will that give me sufficient overhead of expansion?

John.G

Ideally the fill pressure should be 0.3 to 0.5bar higher than the pre charge pressure. You cannot achieve a fill pressure higher than 0.2bar because its fed from the attic header tank so theoretically you need a precharge pressure of 0.2-0.5 or -0.3bar at the EV, impossible. So with a precharge pressure of (now) 1.1 bar and a fill pressure of 0.2bar the boiler pressure at the EV will rise almost immediately to 1.1 bar so effectively you have a precharge and filling pressure of 1.1 bar, assuming a system vol of 100 litres and a 10 litre EV then the max EV pressure when hot will be 1.57bar and boiler pressure might be 1.57+0.2, 1.77bar (no problem). If you were to drop the precharge pressure to 0.7bar (and I wouldn't go much lower, 0.5bar minimum) then the equivalent pressures will ~ be 1.08bar & 1.28bar. Most boilers, gas or oil have a PRV (safety valve) setting of 3bar but Grant are one exception at a setting of 2.5bar so again no problem for you. I assume/hope you have a PRV installed because if not and the EV loses its precharge pressure or gets a holed diaphragm then the sky's the limit!, the pressure on heat up will rise uncontrollably and will certainly do damage.

Aside: Its a pity that we get no email alerts now with the new format boards.

10-10-20

Thanks JohnG. I might drop to 0.8 bar and observe.

It's a 14 radiator system and the EV is 14l. There is a small EV in the back of the boiler (either 5 or 7l), not enough for the house. There is a PRV, but oddly it was never piped outside, so I took the time to complete that job too last month.

Many thanks for your information - I was just using slightly-educated guess-work to get the pressures right (to no loss - I suppose!).

John.G

You can do your own calculations here.

If the filling pressure is < precharge pressure the the calc must be done at the precharge pressure as water is incompressible and will rise to the precharge pressure almost immediately on heating commencement.

Expansion Vessel Calculatios 4.xlsx

The reason for having the filling pressure higher than the precharge pressure is that you will have a nice little reserve of water to make up for any air venting etc without having to top up frequently, you should go for a year or two with no need for top up, some boiler manufacturers including Grant advocated having both the same, this in turn lead to the people leaving the mains pressure reduced to 1/1.5bar via a PRV (pressure reducing valve) the so called auto filling valve on continuously, any real leak(s) in the system then can go undetected leading to sludge/corrosion etc, I have seen pin holed rads less than 3 years old due to this. The filling valve should always be shut after filling/top up.

jambo9421

I've had a look in my attic at the Ev and on the manufacturers label it's 2bar..there isn't a valve on the unit to check the pressure that I can see.it just looks like a flat black plastic cover that I did not want to remove

John.G

Just prise off or unscrew that plastic cover as that's all it is, a dust cover. You will then see a schrader valve, exactly the same as your tyre valve which you can then check. So reduce this to 0.7Bar,if you don't have a pump, be careful in reducing the pressure, only do it in short bursts (with your thumb nail or whatever), even 0.5bar is OK but wouldn't be too happy below this. If its < say 0.3/0.4bar, I would pump it up to 1bar and then reduce it again to 0.7bar, set the filling pressure to 1.5bar, at the boiler.

jambo9421

Thanks John G I'm gonna give that a go over the weekend and will let u know..this might be a silly question but where is all the water going at the min since I don't see any leaks.

Paul_Mc1988

https://www.boards.ie/discussion/comment/118425604#Comment_118425604

The could be leak under the ground floor floor board/concrete. A thermal camera can be used to pick up these leaks I think.

jambo9421

https://www.boards.ie/discussion/comment/118426308#Comment_118426308

When I had the dual open system we never ever had any issues with leaks or pressure variations it always sat around 0.2 bar and never moved.we were told that is the normal pressure for that type of system.so it's only since I got the stove disconnected and the system sealed the issuse of pressure dropping now.hopefully its sumit to do with the ev

John.G

Does the pressure remain at 0.4bar once it falls?.

When re filling to 1.5bar or whatever, does the pressure rise in a very short time, I'm talking about 10 secs or so.

We will get a very accurate handle on the leakage, if any, once we know that precharge pressure.

jambo9421

It seems to stay around 0.4 bar I don't wanna let it go any lower as I'm out at work all day so I keep filling it every fee days..and I wud need to time how quick it fills..the fill loop is up in the hot press upstairs and the gauge is downstairs on the boiler

jambo9421

OK so I went in the attic this morning and checked the pressure on the ev..it was 20psi so I've dropped it down to around 10 psi which I think is 1bar..I've refilled the system to 1.2 bar and have the heating on now so we will see if there is any difference in the pressures..

On a separate note I've got the system power flushed last year and I replaced all the radiator valves and trv last month.i manually flushed any rads I cud..I have one radiator in my kitchen that sometimes gets hot and most of the time doesn't.ive tried to balance the system myself but I'm not a plumber.i have most valves upstairs turned down as they heat 1st and fast..the pipe that doesn't have the trv to the radiator is red hot and the side that has the trv is cold..does that mean they need to be swapped around ??that is the way it always was