Rising pressure woes

[Large human]

Hello
In May I had an ideal logic 15 + condensing boiler fitted onto a pre existing y plan system ( the new boiler is a 15 kw the old one was a 10 or 12 kw not sure as it came with the house).

Since installation hot water demand has been fine running from 1 bar cold to 1.7 bar running.
But ....
When central heating is switched on it rises from 1 bar and within a couple of minutes reaches 3 bar .
The first time it did this the PRV kicked in.

I have last week had a new PRV fitted and a new 8 litre expansion vessel (although the engineer fitted a blue potable vessel when the original was a red one).

I have since tried the heating and it remains to rise in pressure but I switch it off as it gets to 2.5 bar before the PRV kicks in..

Any advice given would be greatly appreciated on what the problem could be.
I will be using a gas safe engineer but a sort of second opinion would be greatly received.

Thanks in advance 🙂

 

[Dotty]

Get him back to check the vessel charge with an empty system.

If it goes again ask him to fit an external vessel. 12 litre would be ample.

 

[Large human]

Thanks for the quick reply... it is an external vessel 8 litre potable. ..its located right next to cylinder...The old red one 8 litre was taken off last week as this was thought to be the cause of the rise in pressure.....He did say it had water in it .......but with the new one on the pressure still rises.......

 

[Large human]

I'll certainly ask him about the pressure charge in new vessel though......

A flush of the system has been mentioned....could this be a way forward????

 

[Ch4 plumbing]

Do as Croppie has suggested, is the expansion vessel on a braided hose? If yes did he replace? IMHO it's better to have expansion vessels on rigid pipe.

 

[chris watkins]

I'll certainly ask him about the pressure charge in new vessel though......

A flush of the system has been mentioned....could this be a way forward????

No, you just need someone who can install & set up a heating expansion vessel.
What is the head of water above the vessel (i.e. how many Metres to the highest rad /towel rail above it)?

Have you got standard panel radiators installed?

And it is only reading 1 bar when cold?

 

[Large human]

Loop metal hose ....vessel to PRV copper pipe and vessel to cylinder its copper pipe ......I'll ask him to check vessel pressure before talking about system flushes then ....

If anything else it could be I have no problems mention it to him as all I want is the thing functioning properly 🙂

 

[Large human]

Thanks for the replies all advice appreciated. ...as I literally know nothing of heating systems

 

[Ch4 plumbing]

If it's a braided hose chances are it's blocked! They are terrible on heating systems!

 

[Large human]

No, you just need someone who can install & set up a heating expansion vessel.
What is the head of water above the vessel (i.e. how many Metres to the highest rad /towel rail above it)?

Have you got standard panel radiators installed?

And it is only reading 1 bar when cold?

Would any heating engineer be able to work all this out....or is it something specialised. ..


The only things I can answer there is yes standard panel rads .

There's no radiators above level of vessel ...The vessel , cylinder pumps and water tank are in a cupboard in one of the bedrooms.. The boiler is downstairs in kitchen.

Think its running at one bar at present cold because I bled some radiators and one had some air in not topped it up since noticing rise in pressure still present with heating on.

 

[Large human]

If it's a braided hose chances are it's blocked! They are terrible on heating systems!

The only braided hose is from filling side would that cause the problem ...its switched off when not needed for actively topping pressure up ....

 

[Simon F]

the answer was in post two.

a potable vessel will come pre charged at 3 bar, possibly more.
so if it has not been adjusted to suit the pressure of the system then is doing nothing

 

[Ch4 plumbing]

No if it's on the filling loop don't worry about it,nalthough it should be removed and capped if not in use.

 

[Best]

I'm not gas, but agree that the braided hose needs checked. They block solid on the oil boilers.
As it is external I would use copper pipe to the expansion vessel.
The fact that the pressure rises immediately, says to me no expansion there at all.
Edit, - forget hose theory, I now see only filling hose used.

 

[Large human]

the answer was in post two.

a potable vessel will come pre charged at 3 bar, possibly more.
so if it has not been adjusted to suit the pressure of the system then is doing nothing

Should any gas safe engineer be able to calculate this and pressurise vessel accordingly

 

[Large human]

Pre charge of this potable vessel is 4 bar max working pressure 10 bar (just found box in bin)

 

[Simon F]

Should any gas safe engineer be able to calculate this and pressurise vessel accordingly

it's not difficult, but!

 

[chris watkins]

Would any heating engineer be able to work all this out....or is it something specialised. .. Any heating engineer


The only things I can answer there is yes standard panel rads . So standard water content for the size of the boiler i.e. amount of expansion should be able to be accommodated by an 8L vessel

There's no radiators above level of vessel ...The vessel , cylinder pumps and water tank are in a cupboard in one of the bedrooms.. The boiler is downstairs in kitchen. System & Vessel charge should be set at no more than 1 bar

Think its running at one bar at present cold because I bled some radiators and one had some air in not topped it up since noticing rise in pressure still present with heating on.

The pressure in the system is set at 1 bar cold fill but more than likely the pressure in the vessel is more than the 3 bar of the safety valve so as the water in the heating system heats up & expands there is no where for it to go so it quickly rises & blows the safety valve. If the vessel pressure was set correctly water would flow into the vessel & the pressure would be kept at little more than 1 to 1.5 bar.

 

[Large human]

Finally got round to getting a different engineer round today 30 mins in total took pressure out of vessel as it was still holding its pre charge of 4 bar and reset to 1.5 bar .....running at a max 1.9 bar ...very happy .....Thank you all especially croppie for hitting nail right on the head early on .......saved me a power flush!

 

[turnpin]

Finally got round to getting a different engineer round today 30 mins in total took pressure out of vessel as it was still holding its pre charge of 4 bar and reset to 1.5 bar .....running at a max 1.9 bar ...very happy .....Thank you all especially croppie for hitting nail right on the head early on .......saved me a power flush!

Thanks for the update Large Human......regards Turnpin😉