Does central heating perform differently at different pressures?

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Let's say we have 2 system boilers on closed systems pressurised within permitted tolerances.

1 pressurised to 0.9bar when cold (reaches approx 1.3 when hot)

1 pressurised to 1.4bar when cold (reaches approx 1.8 when hot)

Will these systems perform differently? Is there a benefit to higher pressures?

Will these systems
 
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In a word no.
Minimum pressure is usually 1bar, much below that and the system will stop operating.
1.4 gives you a bit of slack so to speak so a small loss in pressure (like venting a small bit of air) will not cause the gauge to drop to below 1 bar.

I guess there might be a minutely higher boiling at higher pressure, but as boilers do not in fact boil, because the thermostat keeps them well below 100c it makes no difference in practice.
 
In a word no.
Minimum pressure is usually 1bar, much below that and the system will stop operating.
1.4 gives you a bit of slack so to speak so a small loss in pressure (like venting a small bit of air) will not cause the gauge to drop to below 1 bar.

I guess there might be a minutely higher boiling at higher pressure, but as boilers do not in fact boil, because the thermostat keeps them well below 100c it makes no difference in practice.
Thanks footprints!

Is there any value in having pressure be as LOW as permitted (accepting that a small drop could cause the boiler to shut down).

I'm thinking less strain on joints, valves etc
 
Depends on the boiler. If you have a boiler that uses a pressure switch then running low pressure will give you limited head room, more frequent/little top ups. If the boiler has a flow switch then you can run at a low or zero pressure as they work on flow/circulation not pressure. And having zero pressure doesn't mean the system is empty. If you have a boiler that has neither and uses the temp sensors to determine circulation then in theory you can run at any pressure but they will suffer more abuse when cutting out due to inadequate water quantity, the boiler will be over heating.
 
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Joints are not bothered by pressures within their specifications.

Boilers do actually operate more efficiently when on higher power settings within their range.

When you boil a saucepan of water you will see small bubbles on the bottom. These are steam and insulate the metal from the water.

Inside a boiler this should not occur significantly when within it's specs.

But at an increased water pressure any tendency to produce this steam is much reduced so it would be very slightly better to operate at the upper end of normal pressures, that is 1.5 bar cold.

There is no disadvantage to operate at the higher pressure and several advantages!

Tony
 
One disadvantage of running at a higher pressure is you are then relying on the system water quantity being accurately calculated and dealt with by the expansion vessel at maximum temperature. Quite a few modern boilers with pressure sensors not only trip out on low pressure but also HIGH pressure!
 
Can you remind me of one which trips out at high pressure?
 
Off the top of my head, sime, baxi ga to name two. Causes us a few call outs when customers over pressure their boilers and the boiler stops altogether!
 
Depending on the frictional resistance of the heating circuits, yes. You need to calculate the static head of your system and match pressure to it, including the pressure and capacity of the vessel.
too low a pressure can mean that the pump will not service the extremities of the system.
 

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