Pressure after expansion vessel replacement

[JamiePattison]

We had the expansion vessel replaced as it was filled with water.

A few hours later I noticed the pressure dropped so I topped it up. Next day exactly the same where I'm topping the pressure up every few hours.

I spoke to the plumber who replaced the vessel and he said this is normal and to give it 2 weeks for it to adjust.... Does this sound correct?

 

[Fitzroy]

Not in my experience, system should hold stable pressure equal to the charge pressure of the expansion vessel, assuming filed and well bled to get all the air out.

 

[Bingy man]

I’m going to say was the correct fault diagnosed, so many vessels get replaced for incorrect diagnosis . What was the original problem ? Once the vessel was replaced , filled , and air removed and ran to test - the pressure should not drop . As the system ( rads ) warm up the system pressure will rise slightly but should not go into the red section. In heating mode keep your eyes on the system pressure ( 1.2 1.5 from cold . ) If everything is set up correctly then the pressure could rise to around 2 bar give or take. If the pressure exceeds this eg ( 2.5 -3.0 bar or above ) it’s possible that the capillary tube or hose connecting the vessel to the boiler heating side is blocked or severely restricted. Your pressure safety valve opens at 3 bar and dumps the excess pressure outside. Your system pressure has now fallen and the whole process starts again as you will naturally top the pressure back up when you notice it’s fallen . Another possibility is a leak from the radiator pipework or an internal leak from the main heat exchanger which is unseen as the escape of water drains via the condensce pipework. It only takes a small amount of water to leak out and drop the pressure. Is your filling loop via a small flexible tube and a tap/ valve ? Or is it built into the boiler ? If the valve is not turned off correctly or the valve is passing then this will increase the system pressure which will activate the safety valve if it pushes the system pressure above 3 bar .. long post but a few of the possible causes of pressure loss ..

 

[Sideways]

I agree with the guys above but the one caveat, that the system was properly bled after the expansion vessel was swapped, is important.
If the plumber didn't or wasn't able to get all the air bubbles out of the system at the time, then these should be swept around the system and may eventually be released at an automatic air vent if you have one.

If enough (a lot) of trapped air was involved, this might end up affecting the pressure but repeated pressure drops and top ups in under 24 hrs sounds like they did something wrong. Call them back.

I have a late 70's house with solid concrete ground floors and all the downstairs radiators are fed by drops from above. Most of the plumbing is under the upstairs floors. These are notorious for getting air locks and bubbles whenever the system is partially drained so I've fitted 4 automatic air vents in addition to the one in the boiler and self bleed valves in all of the radiators. These get rid of most of the air bubbles within a few minutes but small ones can still take days to get rid of. These small bubbles don't cause a drop in pressure because they are small compared to the expansion vessel.

 

[Bingy man]

The but that makes me dubious is - “ give it 2 weeks to adjust “ rather than - I’ll call back round check everything is ok ( giving the cust piece of mind and reassurance- whilst at the same time checking you haven’t done anything daft like left the filling loop partially open or the drain off isn’t fully closed ( easy to do after a long day )

 

[Bingy man]

I agree with the guys above but the one caveat, that the system was properly bled after the expansion vessel was swapped, is important.
If the plumber didn't or wasn't able to get all the air bubbles out of the system at the time, then these should be swept around the system and may eventually be released at an automatic air vent if you have one.

If enough (a lot) of trapped air was involved, this might end up affecting the pressure but repeated pressure drops and top ups in under 24 hrs sounds like they did something wrong. Call them back.

I have a late 70's house with solid concrete ground floors and all the downstairs radiators are fed by drops from above. Most of the plumbing is under the upstairs floors. These are notorious for getting air locks and bubbles whenever the system is partially drained so I've fitted 4 automatic air vents in addition to the one in the boiler and self bleed valves in all of the radiators. These get rid of most of the air bubbles within a few minutes but small ones can still take days to get rid of. These small bubbles don't cause a drop in pressure because they are small compared to the expansion vessel.

I always advised the customer that after a drain down you can expect some air to remain in the system which would often find its way into the rads . The system should be used as normal but to ( vent ) the rads after a couple of days ( not weeks ) and to top up the pressure as reqd . They should also expect a little system noise ( trapped air ) while it settles down ( this avoids false and unnecessary call outs ) I would then call them back after 4/5 days to check if all is ok ( this promotes trust that you care about your work and not just in it for the money ) any remaining issues can then be addressed and resolved usually by way of advice. End of the day your customers are your bread and butter and they can make or break you depending how you engage with them .. imho of course

 

[JamiePattison]

So far what we've noticed is when the hot water/heating is turned on the pressure rises..... When it cools it comes down. He's now accepted to come and look.

The questions asked were, if there are any leaks around the boiler or radiator. Thanks again everyone

 

[Spectric]

We had the expansion vessel replaced as it was filled with water.

To prove the bladder had gone in the expansion vessel you would remove the valve core and water should exit, how old was the expansion vessel ?

They are a sealed system, ie once filled and to pressure then the pressure will move slightly upon heating / cooling but if you are having to top it up every few hours then you have a loss of water or a leak, the water is going somewhere and the pressure release valve is an obvious culprit. Have you checked the discharge pipe for signs of water ?

when the hot water/heating is turned on the pressure rises..... When it cools it comes down

By how much ? If it is rising to high then the expansion vessel is not accomodating the excess volume of water upon heating and so the pressure release valve will open to prevent the pressure getting to high, we are assuming the expansion vessel is of the correct size as the old one !

 

[JamiePattison]

To prove the bladder had gone in the expansion vessel you would remove the valve core and water should exit, how old was the expansion vessel ?

They are a sealed system, ie once filled and to pressure then the pressure will move slightly upon heating / cooling but if you are having to top it up every few hours then you have a loss of water or a leak, the water is going somewhere and the pressure release valve is an obvious culprit. Have you checked the discharge pipe for signs of water ?


By how much ? If it is rising to high then the expansion vessel is not accomodating the excess volume of water upon heating and so the pressure release valve will open to prevent the pressure getting to high, we are assuming the expansion vessel is of the correct size as the old one !

The expansion vessel was probably around 14 years old. It was added when the house was built.

I don't see a leak anywhere, the only place I have looked is around the house by the radiators. Is there anywhere else I can look at to see if there is a leak? Unfortunately I don't know what or where this discharge pipe is but happy to look if you can describe it?

I've attached an image of the pressure gauge. This morning it was at 0 and the boiler was off with a warning light. I raised the pressure just before the red line and then turned the heating/water on to heat up and it went to 0 and just above. Once it cools it goes below the red line. Not sure if this is any relevant.

 

[Sideways]

That red knob directly below / behind the pressure gauge in your photo looks like a pressure relief valve.
They are spring loaded, partial turn against the spring to test / release some water.

There may well be other red knobs like that elsewhere, but that's one of the possibles.

With all this venting, refilling going on, make a note to put a fresh bottle of corrosion inhibitor in the system as soon as the leak is resolved.

 

[Spectric]

I don't see a leak anywhere, the only place I have looked is around the house by the radiators.

If a system is not holding pressure then your heating engineer needs to attach a pressure tester that will pump the system up and then go look for the leak. If the pressure release valve is not the issue then look at auto air vents and radiators, look for tell tale signs like damp floors under radiators because radiators will corrode out and it is surprising how much loss you get through a pin hole caused by corrosion. That water you add to regain the pressure is the same amount that is leaking somewhere, you need to find it before it might become a bigger issue.

As @Sideways has said, you then need to add the corrosion inhibitor as soon as the system is leak free.