Combi when cold = 1.7 bar, when hot= 2.6 bar

[robbieee]

Having a few pressure issues with my 24i RSF combi boiler. My plumber has added a radiator to the system. It was then repressurised, bled then topped up again.

However I have noticed that the pressure when cold is dropping 0.1bar over a couple of days. I cant find a leak anywhere. When the system is hot, the pressure increases to 2.6bar. Is this normal? Do i have an airlock?

The plumber is next to useless so i dont want to get him back!

 

[ianmcd]

Your expansion vessel needs re-charged or you have a blockage in your communication tube/hose between your boiler and your vesell , get a proper experienced engineer to look at your boiler and mention the over pressurisation,

 

[robbieee]

Would that explain the pressure dropping when cold?

 

[Dan Robinson]

yes

 

[robbieee]

This really angers me... I just spoke to the plumber there and he said "I cant think anything that would cause that, keep an eye on it- you might have a problem with your expansion vessel"

I have already paid this guy, should i insist he comes back up to recharge the expansion vessel?

(Thanks for all your help guys!)

 

[Dan Robinson]

How many rads have you got now?

Roughly how big are they?

That boiler is getting on a bit and the vessel could well be on its way out.

 

[MANDATE]

It is normal for the pressure to increase when heating is operating.
The water expands and increases its volume. The additional volume goes into the expansion vessel. The vessel should contain only 'air'. The diaphragm is pushed to the system side using air pressure of approx 1bar to ensure the max amount of air, this before setting the water pressure to approx 1bar.
When the water is expanding the 'air' gets compressed and its pressure rises and so does the water pressure.
The amount of rise depends on volume of water in system and the size of the expansion vessel. the rise would normally be in the region of 1 to 1.5bar.
If the expansion vessel has lost any of its pre charge it is most likely to have a reduced volume of air for compression. The result of reduced volume is it goes to a higher pressure. However a pressure relief valve set to 3bar is in place to ensure the system is not subject to anything higher.
What comes to mind is
Adding a radiator and pipe work increases the system volume.
Before re pressurising the water, did plumber check the expansion vessel air charge pressure.
Has the pressure relief valve been opened because once opened they don't always seal fully and that may account for your leak which you cant find.
It would be wise to clean the prv, but doubt if you could dismantle it without specially thin spanner, most plumbers just opt to fit a replacement

 

[sooey]

This really angers me... I just spoke to the plumber there and he said "I cant think anything that would cause that, keep an eye on it- you might have a problem with your expansion vessel"

I have already paid this guy, should i insist he comes back up to recharge the expansion vessel?

(Thanks for all your help guys!)

It's not the plumbers fault if you have a problem with your expansion vessel.

 

[robbieee]

How many rads have you got now?

Roughly how big are they?

That boiler is getting on a bit and the vessel could well be on its way out.

I have 11 radiators now

 

[robbieee]

It is normal for the pressure to increase when heating is operating.
The water expands and increases its volume. The additional volume goes into the expansion vessel. The vessel should contain only 'air'. The diaphragm is pushed to the system side using air pressure of approx 1bar to ensure the max amount of air, this before setting the water pressure to approx 1bar.
When the water is expanding the 'air' gets compressed and its pressure rises and so does the water pressure.
The amount of rise depends on volume of water in system and the size of the expansion vessel. the rise would normally be in the region of 1 to 1.5bar.
If the expansion vessel has lost any of its pre charge it is most likely to have a reduced volume of air for compression. The result of reduced volume is it goes to a higher pressure. However a pressure relief valve set to 3bar is in place to ensure the system is not subject to anything higher.
What comes to mind is
Adding a radiator and pipe work increases the system volume.
Before re pressurising the water, did plumber check the expansion vessel air charge pressure.
Has the pressure relief valve been opened because once opened they don't always seal fully and that may account for your leak which you cant find.
It would be wise to clean the prv, but doubt if you could dismantle it without specially thin spanner, most plumbers just opt to fit a replacement

He didnt check anything before re pressuring. He just done the work then repressurised.

As far as i know it hasnt got more than 3bar sot he pressure relief hasnt opened. This valve is only 9 months old as it was replaced due to the old one leaking.

 

[robbieee]

This really angers me... I just spoke to the plumber there and he said "I cant think anything that would cause that, keep an eye on it- you might have a problem with your expansion vessel"

I have already paid this guy, should i insist he comes back up to recharge the expansion vessel?

(Thanks for all your help guys!)

It's not the plumbers fault if you have a problem with your expansion vessel.

He installed the radiator with the 15mm copper pipe at an angle going into the TRV. It leaked. He came back to fix. Twice.

I should just get someone else in

 

[sooey]

He didnt check anything before re pressuring. He just done the work then repressurised.

Did you ask him too? When was the boiler last serviced? Would you expect a garage to check engine oil when you ask them to change your front brake pads?

 

[Dan Robinson]

I would say 11 average rads would be too much for the boiler's internal vessel.

Especially one as old as the one in your boiler.

A bit of pressure increase is perfectly normal during a heat cycle. But anything over half a bar I would say is excessive.

 

[robbieee]

He didnt check anything before re pressuring. He just done the work then repressurised.

Did you ask him too? When was the boiler last serviced? Would you expect a garage to check engine oil when you ask them to change your front brake pads?

Surely he would fire up the boiler and he would notice it then? He didnt even turn the heating on!!

I can understand the pressure increase when hot if its the expansion vessel that needs recharged. But what about the pressure drop when cold? I dont understand why that would be happening?

What causes the expansion vessel to lose air? Faulty expansion vessel? Costly to replace?

 

[onlyfitidealboilers]

Half a bar. 1.0 bar cold 2.0 hot is perfectly normal. Most vessels are charged to 0.8 of a bar as well.