central heating - open or closed?

[lxbn]

I am having a loft conversion with 4 extra radiators added to the system and a megaflow system fitted.

The present central heating system is an open system with expansion tank in the loft. The boiler is a fairly new Worcester Bosch, can be converted to a closed system boiler and up to the the job. I don't mind having an expansion tank in the loft space but there might be issues of where it goes as it should be I think about a metre above the highest radiator - although this may be overcome by putting in lower level radiators in the loft.

Some radiators in the system are of the older panel type but work great. Does conversion to a closed system mean that the system must be high pressure tested - my installer, who is G3 registered, assures me that in his experience leaks have been few and not major.

My question is, are what are the advantages/dis-advantages of having a closed system as opposed to an open system.

 

[ChrisR]

I would:
Test the water. If it's grubby, put a cleaner in for a week then flush it clean.
Look hard at the rad valves, change any which look a mess or show signs of having leaked.
Are there any "slow" or inadequate rads? If so now's the time to change them, unless it's just tsludge.
Pressure test the system, cold, without a pressure vessel connected. That way leaks show up rapidly. Find any leaks. They'd probably be on rad valves, anywhere else and they need fixing.
Pressure test the hot and cold water distribution pipes while the machine's out, because that'll be on the mains now too.

Add inhibitor and seal the system, and it'll stay pretty cleaner than it would open, and may run quieter.

 

[Agile]

I agree that rads rarely leak when converted to a pressurised system.

Rad valves often do though.

There are two kinds of rad valves, the best ones have a nut which compresses the seal and can be adjusted. The worst ones have a rubber "O" ring seal which have to be replaced if they leak.

In many ways any older rad valves and all "O" ring types are better replaced before it is converted.

A pressurised system has an improved efficiency of about 2% but they do need the occasional topping up by the user.

Tony

 

[lxbn]

Thanks.

Think I'll talk to my iinstaller about converting to a closed system - I'll have to put up with losing some space in the airing cupboard for the expansion vessel but it may be worth it.

Am I right that on a closed system you do not bleed radiators and the only thing you need to do is occassionally (perhaps once a year) check the system to make sure the pressure level is ok and if necessary open the valve to bring up the pressure.

If in future you want to change a radiator, do you drain the system and then refill as a normal system?

 

[Agile]

The expansion vesel can be fitted anywhere on the system as long as its within the thermal envelope of the building.

As with any system, changing a rad only requires the rad valves to be turned off.

Tony