Advantages of sealed CH system over vented

garyo · 22 Jul 2019

I'm in the process of replacing a 35 year old conventional (vented system with vented HW cylinder) boiler with a Grant Vortex Pro. My plumber is pricing it all up and strongly recommend that I also seal the system at the same time, and said it'd run far cleaner without a header tank.

It doesn't make much different cost wise, so my only concern is that parts of my pipework are buried in screed with 35 year old compression fittings. They haven't caused me problems so far, but I wonder if I'd be applying additional pressure increase for little/dubious benefit? He said that the sealed systems can be set to low pressure so I shouldn't need to worry about it...

How much pressure difference would there be in reality? Am I worrying over nothing?

Thanks

bernardgreen · 22 Jul 2019

If the surface of the water in the F&E tank is 32 feet ( 10 metres ) above the pressure gauge then the gauge will read 1 bar ( if the gauge is accurate ).

If the present F&E tank is 16 feet above the lowest central heating pipe joint then the pressure at that joint will be 0.5 bar. So if the system is sealed and set to 1 bar the pressure at those joints will be doubled.

rhinosaw · 22 Jul 2019

I am going thru the same dilemma myself, an ancient system going pressurised, I would go for open vented again but it is not possible because the f& e tank is no higher than the boiler.
So I have no choice but take the risk.
Chances are u will be ok but the risk is there and when u look at Bernard's calculations it looks even more scary.
I have found that installers will push u to go combi.

ScottishGasMan · 22 Jul 2019

In the system you describe I wouldnt dream of going sealed. Even running a sealed system at 0.9bar, still has the possibility of going up to a little over 3bar in the event of different faults (ones that do happen not just far flung possibilitys)

So my advice would be stick to open vented. It wont make much difference on how clean the system runs if its a correctly set up open vented system with some inhibitor in it (check concentration and top up inhibitor on service and should be no issue with dirt as long as its well flushed out initially)

Failing that, the other inbetween option can be to run the system using a plate heat exchanger. So for example, moving from old open vent system with cylinder to a combi, you can still use the combi and put it under normal sealed pressure, that water is then fed to a plate heat exchanger and the open vented system is heated off the plate at normal open system on that side of it, literally just needs a 2nd pump and plate fitted to make it work.

wwwebber · 23 Jul 2019

Went with sealed and haven't looked back. System is more efficient, heats up faster and now my loft is free of tanks full of water

ianmcd · 23 Jul 2019

wwwebber said:
Went with sealed and haven't looked back. System is more efficient, heats up faster and now my loft is free of tanks full of water

yes but not suitable for all systems, I certainly wouldnt recommend that the OP changes to a sealed system

garyo · 23 Jul 2019

Thanks chaps. I suppose the other thing I could do is cap off the F/E tank and pressure test the system at 3 bar for an hour. I'd have to do that before the plumber could know which model of boiler to order though, so the sequencing of work gets a little complicated but still feasible I suppose.

ianmcd · 23 Jul 2019

garyo said:
Thanks chaps. I suppose the other thing I could do is cap off the F/E tank and pressure test the system at 3 bar for an hour. I'd have to do that before the plumber could know which model of boiler to order though, so the sequencing of work gets a little complicated but still feasible I suppose.

But if you do that and force a leak, there is no guarantee that the leak will stop when you connect it back up to an OV system, I would go for the Plate heat exchanger system if it was me

bernardgreen · 23 Jul 2019

wwwebber said:
System is more efficient, heats up faster

The new boiler may be more efficient at heating water flowing through it. Hence the system would appear to be more efficient but not because the water is pressurised.

wwwebber said:
and now my loft is free of tanks full of water

that is about the only practical advantage of unvented, but you have only swapped one tank in the loft for a more complex tank ( expansion vessel ) often fitted inside the boiler. Can be a real pig to service on the annual service needed to ensure the unvented system is safe.

The other large tank ( cold water ) comes in handy when the water supply is cut off. It enables you be able to flush toilets.

aptsys · 24 Jul 2019

wwwebber said:
Went with sealed and haven't looked back. System is more efficient, heats up faster and now my loft is free of tanks full of water

What's the logic behind this statement? Why would a sealed system be more efficient and heat up faster?

dilalio · 25 Jul 2019

ianmcd said:
I would go for the Plate heat exchanger system if it was me

Done two of those so far this year - on big ass houses with all kinds of ancient pipework all over the place. It works a treat

Just make sure the CH plate hex is well supported and insulated.

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Advantages of sealed CH system over vented

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