Worcester 26cdi extra pressure issue maybe

[Iori]

I have a Worcester CDi Extra Combi boiler, which had a pressure problem that I sorted thanks to reading this forum. I now have a question regarding fine tuning the system.

First - this is what I have already done.

Identified that the bladder in the original expansion vessel had failed, (water leaking through the schroeder valve) due to the system overpressurising the pressure valve also was leaking - constantly (pressure would drop to zero within about 36 hours irrespective of boiler demand.)

The boiler had an 8lt expansion vessel as standard, I replaced this with an external 12lt expansion vessel and blanked the pipe to the original internal expansion vessel. I also replaced the PRV.

I then set the pressure in the expansion vessel to 0.75 BAR and refilled the CH system, by the time I had bled all the air from the system i ended up with an initial cold system pressure of 0.95 BAR decided to leave it at this for the time being.


Thats the background - Now for my question

It's been over two weeks since i did the above work, in that time the COLD system pressure has remained constant at 0.95 BAR whilst the HOT system pressure is 1.25 BAR. The radiators upstairs seem to be slightly cooler than the ground floor rads but only marginally, hoping to get a temp gauge on them in the next few days (when i find it in my garage!!!) to measure accurately but its no more than a few degrees.

To me the pressure differential between hot and cold does seem a bit low, do I need to increase the cold system pressure or raise both expansion vessel and cold system pressure, or do I be really happy that I have a CH system with very little issues and leave well alone? I look forward to your views on this.

When the system was originally put in I was quite anal about it and actually balanced all the rads so that the temp drop across each rad was equal even though the plumber said it wasn't necessary.

My System
Worcester 26 CDi Extra Combi situated downstairs in the utility.
5 radiators downstairs
5 radiators upstairs
ext 12lt expansion vessel situated directly underneath the boiler teed into the CH return
EV pressure 0.75 BAR
Cold system pressure 0.95 BAR.

Regards
Iori
'if it ain't broke I can fix it'

 

[kevplumb]

The boiler had an 8lt expansion vessel as standard, I replaced this with an external 12lt expansion vessel and blanked the pipe to the original internal expansion

To me the pressure differential between hot and cold does seem a bit low,

seeing as you have upped the size of the ex vessel

the expansion now has a third more space to fill



i would say leave it alone

 

[45yearsagasman]

Increasing the system pressure will not really achieve anything other than to put more strain on components.You sound like you know a fair bit about how your system works so you could try another session of balancing and make sure system is vented of all air.Pressure diff is not an issue and your charge settings sound ok.Don't forget you have increased the EV from 8 to 12 which will have a bearing on those pressure readings.
Just seen Kev has posted and I agree.

 

[kevplumb]

i was gonna say that

 

[mrgas]

The pressure differential between cold and hot is fine and an indication of a healthy expansion vessel.
The smaller this differance the better!
You could reduce the system pressure to match the expansion vessel pressure.
Remember that pressure gauges arnt totally accurate.

 

[PEDANTICVINDICTIVEMAN]

If it ain't broke don't fix it

 

[Iori]

Thank you all for your replies, will re balance the sytem and check for any more air tomorrow, will let you know how I get on, but for now I have much more important things to attend to - I'm off fishing for the night!

Ior

If it ain't broke I'll fix it.