Boiler Question - Pressure

darktrader · 18 November 2008 at 11:26AM

Worcester 28CDI

Serviced every year - BG Scheme.

Pressure gauge used to be 1 bar at rest, 2 - 2.5 bar when Central Heating on.

Problem was:-
Would not drop below 2 bar. Went up to almost 4 bar when operating.

BG Engineer came. Did various things including a "recharge" if I have that right? - OK for a week. Now, won't go below 2 bar at rest, but only goes to 3 bar when operating. Like this for a fortnight. (Also, might just be coincidence, but the rads, which were always hot - great system - are now even hotter. But the engineer did clear out some air locks in the System.)

Question:

Do I need to call them back out? What is the worse case scenario? If I need to call them back out I would prefer to leave it to the New Year - only because I will have more holiday then and won't lose money from work.

All through this, heating and hot water both work fine.

Please advise.

ThrifTE · 18 November 2008 at 1:49PM

I wouldnt worry about it, you can try your radiators see if they are cooler at the top than the bottom, if so you can bleed the air out a little until you get a dribble of water, keep an eye on the pressure gauge, if you let too much pressure out of the system you will need to re fill it. but it is probably just the remaining air in the system causing this. you might find it is only one radiator that is cooler at the top then the bottom.

darktrader · 18 November 2008 at 1:54PM

ThrifTE wrote: »

I wouldnt worry about it, you can try your radiators see if they are cooler at the top than the bottom, if so you can bleed the air out a little until you get a dribble of water, keep an eye on the pressure gauge, if you let too much pressure out of the system you will need to re fill it. but it is probably just the remaining air in the system causing this. you might find it is only one radiator that is cooler at the top then the bottom.

Thanks. All the rads are very, very hot near the top. Bleed any of them and it's water immediately that emerges, no hissing of air.

bockster · 18 November 2008 at 2:37PM

inside your closed system there should ideally be no air, however because water expands when hot it needs to expand somewhere, this is where your expansion vessal comes in, part of your boiler, and what i suspect the engineer recharged. the expansion vessal has an 'air bag' in it which will be charged to, eg, 0.5 bar when no water in system, when you fill system water 'squashes the' air a little but more so when it gets hot, ie, takes the expansion. it also has the effect of compensating for any small leaks because, as you can't compress the water, any small leak would result in no pressure in system if it weren't for the air in the 'bag' expanding and compensating.

as far as pressure goes, any air in the rads might as well be the same as having a bigger expansion vessal.
your varying pressures has come about by charging the expansion vessal and eliminating air in rads. when all is well you shouldhave approx 1bar cold, more but not in the red when hot. or more exact figures from your manual.

hope this is understandable and helps.

darktrader · 18 November 2008 at 4:26PM

bockster wrote: »

inside your closed system there should ideally be no air, however because water expands when hot it needs to expand somewhere, this is where your expansion vessal comes in, part of your boiler, and what i suspect the engineer recharged. the expansion vessal has an 'air bag' in it which will be charged to, eg, 0.5 bar when no water in system, when you fill system water 'squashes the' air a little but more so when it gets hot, ie, takes the expansion. it also has the effect of compensating for any small leaks because, as you can't compress the water, any small leak would result in no pressure in system if it weren't for the air in the 'bag' expanding and compensating.

as far as pressure goes, any air in the rads might as well be the same as having a bigger expansion vessal.
your varying pressures has come about by charging the expansion vessal and eliminating air in rads. when all is well you shouldhave approx 1bar cold, more but not in the red when hot. or more exact figures from your manual.

hope this is understandable and helps.

Thanks. Helpful.

Seems there is nothing to concern me, but Now, won't go below 2 bar at rest, but only goes to 3 bar when operating.
It's just the fact that it stays at 2 bars rather than 1 - which has been "normal" for 7 years.

The engineer tested the "overflow" when they were there, so I know if it goes really high nothing can blow up.

darktrader · 21 November 2008 at 10:49AM

Any "experts" out there?

Just read the manual and it states "until Pressure gauge reaches 2.5 bar." When installing.

So, been at 1 bar - at rest - since installation. Engineer set it at 1.3 bar - fixed red needle. Now it never goes below 2 bar at rest - moves to over 3 bar when operating.

Although everything is working I need to know if the pressure at rest is "too high" and will it eventually damage something?

bockster · 21 November 2008 at 4:44PM

the only way to get the pressure down is to let out some water. do it when cold until needle says 1 bar. maybe there is manual override on the over pressure valve which will make it easy.

EliteHeat · 21 November 2008 at 4:57PM

If you have a drain-off valve then open it when the system is cold until the pressure goes down to 1 bar.

if you haven't then use a radiator bleed valve - this is a bit messy though.

The previous explanation re the expansion vessel was spot on.

kaya · 21 November 2008 at 5:35PM

if your heating and water are working why are you concerning yourself with the reading of a cheap 7 year old taiwanese made pressure gauge which is probably way off anyway?, im an engineer and only check mine if it all goes pear shaped, you will have a pressure release valve on your boiler somewhere if your that worried about it, find where it is in the boiler manual, pull/push as appropriate until pressure drops to desired reading, hey presto

Canucklehead · 21 November 2008 at 6:22PM

kaya wrote: »

if your heating and water are working why are you concerning yourself with the reading of a cheap 7 year old taiwanese made pressure gauge which is probably way off anyway?,

'Cos it's the only way you can tell what pressure might be in the system? (Unless you have digital as well.)

, you will have a pressure release valve on your boiler somewhere if your that worried about it, find where it is in the boiler manual, pull/push as appropriate until pressure drops to desired reading, hey presto

Now you have carp under the PRV seating and it won't stop dripping/losing pressure.Good move!

Corgi Guy

economiser · 21 November 2008 at 7:45PM

kaya wrote: »

you will have a pressure release valve on your boiler somewhere if your that worried about it, find where it is in the boiler manual, pull/push as appropriate until pressure drops to desired reading, hey presto

I would never manually operate the PRV, as Canucklehead says you stand a high risk of getting some muck on the valve seat and it could be very difficult to get it to seat properly again. There should be a drain connection on the boiler you can use if you want to drain some water out but if its working OK let it be.

Boiler Question - Pressure

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