Search the forum,

Discuss Cast Iron Radiator Pressure Problems in the Central Heating Forum area at PlumbersForums.net

Messages
4
Hello,

I am hoping to gain some advice following encountering several issues which I'm struggling to determine the magnitude of in my central heating system. I had 8 new cast iron radiators installed in December and since then my Vokera 28 Compact boiler has been dropping pressure on a regular basis.
  • The boiler drops pressure of around 0.5 to 1 bar every 24 hours since the radiators were installed. It is normally pretty stable when the heating is on but will fall considerably during the night when off.
  • The pressure gauge on the boiler takes a while to register when being refilled. When being filled initially the gauge will not move, then a few minutes later it will rise to a stable reading so it's very difficult to know how much to fill but this was the case even before the cast iron fittings.
  • There is some very slight weeping from a bush end at where the brass bleed nipple is on the radiator. I noticed it earlier and it was just a bubble of water that I could blow off.
  • My installer fitted 3 of the 8 radiators TRVs on the return side rather than the flow. The TRVs are Bentley traditional style that are bidirectional but the manufacturer recommends that they are fitted on the flow.
  • The total water content of my new radiators is 90 litres and I have 2 double convector radiators (600*600, and 1200*600), and 3 bathroom towel rails so bringing the total litres in the system above the maximum 78 litres listed in the installation book of the boiler.
Can anyone help me with what, if any, of these potential problems would be causing the pressure to drop?
 
Does the pressure just cycle up and down as it warms and cools? or does it go down over time? There will be some variation in pressure from warm to cold.

Did the installer fit an additional expansion vessel when the cast iron rads were added? As you noted, the expansion vessel in the boiler is too small for that amount of water, and it could lose water from the pressure relief valve when it heats up and water expands and the expansion vessel cannot accommodate it.

Have you talked to your installer about it?
 
Does the pressure just cycle up and down as it warms and cools? or does it go down over time? There will be some variation in pressure from warm to cold.

Did the installer fit an additional expansion vessel when the cast iron rads were added? As you noted, the expansion vessel in the boiler is too small for that amount of water, and it could lose water from the pressure relief valve when it heats up and water expands and the expansion vessel cannot accommodate it.

Have you talked to your installer about it?
Thanks a lot for the reply.

No additional expansion vessel was fitted. I have talked to installer who repumped the expansion vessel but also has now noticed that the heating exchanger is damaged. He thought the repumping would work but it seems to be dropping rapidly ( to 0 from 2 in less than 5 hours) now only when the boiler is off.

Given I’ve been having to pressurise regularly for around a month I’m starting to think I originally had an expansion pressure problem but the. lost enough inhibitor to create some problems with a mixture of the cast iron radiators and the heat exchanger?

I’m loathe to start fixing this thing with expensive repairs only to add additional expansion as well. Attached some pics of the heat exchanger to welcome some thoughts on if this could be why I’m seeing stable pressure when on but rapid falls when off
 

Attachments

  • 8742DE31-D9A9-4E05-85EB-BBE9CFBF2DB6.jpeg
    8742DE31-D9A9-4E05-85EB-BBE9CFBF2DB6.jpeg
    545.1 KB · Views: 7
  • F1092E90-89CF-4044-9A1C-A83E62B97EC6.jpeg
    F1092E90-89CF-4044-9A1C-A83E62B97EC6.jpeg
    474.8 KB · Views: 7
  • 3C5D45BA-370E-460D-BBEB-FA0A6C80A57B.jpeg
    3C5D45BA-370E-460D-BBEB-FA0A6C80A57B.jpeg
    461.5 KB · Views: 7
It is very unlikely that lack of inhibitor would create significant damage in a month, especially if the system is closed and started with inhibitor already.

Is that heat exchanger now leaking? If so, it is more likely the exchanger was close to rotting through, and the additional pressure caused it to spring a leak.

Whether you repair or replace, with cast iron rads you are going to need an additional expansion tank, most modern boilers are not designed for that volume of water. Besides, external tanks are cheap, maybe 50 pounds max.

Really your installer should have fitted an external expansion tank when they added the cast iron radiators. Although the additional pressure from the lack of sufficient expansion vessel capacity may have caused that exchanger to blow through a little sooner rather than later, it likely would have happened in the near future anyway.
 
It is very unlikely that lack of inhibitor would create significant damage in a month, especially if the system is closed and started with inhibitor already.

Is that heat exchanger now leaking? If so, it is more likely the exchanger was close to rotting through, and the additional pressure caused it to spring a leak.

Whether you repair or replace, with cast iron rads you are going to need an additional expansion tank, most modern boilers are not designed for that volume of water. Besides, external tanks are cheap, maybe 50 pounds max.

Really your installer should have fitted an external expansion tank when they added the cast iron radiators. Although the additional pressure from the lack of sufficient expansion vessel capacity may have caused that exchanger to blow through a little sooner rather than later, it likely would have happened in the near future anyway.
It is very unlikely that lack of inhibitor would create significant damage in a month, especially if the system is closed and started with inhibitor already.

Is that heat exchanger now leaking? If so, it is more likely the exchanger was close to rotting through, and the additional pressure caused it to spring a leak.

Whether you repair or replace, with cast iron rads you are going to need an additional expansion tank, most modern boilers are not designed for that volume of water. Besides, external tanks are cheap, maybe 50 pounds max.

Really your installer should have fitted an external expansion tank when they added the cast iron radiators. Although the additional pressure from the lack of sufficient expansion vessel capacity may have caused that exchanger to blow through a little sooner rather than later, it likely would have happened in the near future anyway.
It is very unlikely that lack of inhibitor would create significant damage in a month, especially if the system is closed and started with inhibitor already.

Is that heat exchanger now leaking? If so, it is more likely the exchanger was close to rotting through, and the additional pressure caused it to spring a leak.

Whether you repair or replace, with cast iron rads you are going to need an additional expansion tank, most modern boilers are not designed for that volume of water. Besides, external tanks are cheap, maybe 50 pounds max.

Really your installer should have fitted an external expansion tank when they added the cast iron radiators. Although the additional pressure from the lack of sufficient expansion vessel capacity may have caused that exchanger to blow through a little sooner rather than later, it likely would have happened in the near future anyway.
Thanks again.

I can’t see or feel a leak from the heating exchanger and to be honest I’ve never seen one before he opened it to check it so was hoping someone could tell from the pics I posted if it was the likely fault. The installer thought when he blew up the expansion that we’d get some time out of the heating exchanger but it the pressure has continued to drop at the same rate.

When reading previously about pumping an expansion valve I noticed most people saying to empty the system but he didn’t which I thought was a bit strange. The heating was on so he turned the boiler off at the wall and checked the pressure which was reading 0 then got a foot pump to pump it.
 
Thanks again.

I can’t see or feel a leak from the heating exchanger and to be honest I’ve never seen one before he opened it to check it so was hoping someone could tell from the pics I posted if it was the likely fault. The installer thought when he blew up the expansion that we’d get some time out of the heating exchanger but it the pressure has continued to drop at the same rate.

When reading previously about pumping an expansion valve I noticed most people saying to empty the system but he didn’t which I thought was a bit strange. The heating was on so he turned the boiler off at the wall and checked the pressure which was reading 0 then got a foot pump to pump it.
You don't need to drain the system to charge the expansion vessel, you just need to make sure there is no pressure on the wet side if you want to charge it to the correct pressure.

I would get an external expansion vessel fitted. You mentioned before that the expansion vessel in your boiler is good for 76 litres total system volume, and you know you are well over that, so your installation is currently outside the manufacturer's specifications, and requires an external vessel.

A typical symptom of having too little expansion is the pressure rising more than normal when the system heats up, and it will lose water out the pressure relief valve when it gets too high. Then after it cools down the pressure will lower than it was before.
 
Just had another thought that I was hoping you could help with again. At the weekend, I accidently filled my boiler too much to just over 3 bar following the issue I have with my pressure gauge being slow to respond.

It was ever since then that I've been having rapid pressure drops rather than the every 2 days or so. Could it be that my PRV has passed water and now hasn't sealed properly so it rapidly losing pressure only when off?
 
It is possible for a PRV to dribble after it has let by, and if that has happened it will likely need to be replaced. Have them check that when you get the external expansion tank added.
 

Reply to Cast Iron Radiator Pressure Problems in the Central Heating Forum area at PlumbersForums.net

Creating content since 2001. Untold Media.

OFFICIAL SPONSORS

OFFICIAL SPONSORS

Back
Top
AdBlock Detected

We get it, advertisements are annoying!

Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website. For the best site experience please disable your AdBlocker.

I've Disabled AdBlock