Choosing boilers (again), system vs non-system, W-Bosch vs Glowworm

[Dave]

HELP! I'm trying to decide between boilers again but it's finally crunch time and I need to buy this week.

Looking at

I'm puzzled by the fact that system boilers are cheaper than the equivalent non-system boiler; this doesn't seem logical because there's an extra pump, expansion vessel and safety valve in the system boiler. Does it just reflect sales volumes or is there something more subtle?

There seems to be nothing between the W-Bosch 28HE and Glow worm 30SXI; prices and features are all similar BUT both have fixed-speed pumps rather than self adapting pumps (e.g. alpha) - is this likely to be a problem with a 3 zone (+ DHW) system? The alternative is a non-system boiler 29HE or 30HXI but that's another £140+ for the boiler, alpha pump, expansion vessel, etc.

Any suggestions on how to choose (other than availability) between W-B, GW or ... ???

[Alex]

System boilers are used in conjunction with pressurised hot water tanks such as megaflow,this may be why they are cheaper,and because they are so expensive this reflects in the cost.

[Tony Eva]

Are you sure? I have a Glow-worm 30SXI in a conventional sealed system with indirect HW cylinder. It seems to work perfectly well.

The system is too new for me to comment on the boiler's reliability, but otherwise I am very happy with it.

[Doctor Evil]

A system boiler has:

- an integral pressure vessel

- integral pump.

Heating boilers: are basic boilers with no pump or pressure vessel, that usually can be pressurised, by a kit or external pressure controls and pump or can be open vented. Most buy them to be open vented.

A combi is a system boiler with and added water section.

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[Alex]

A System Boiler (SXI) for use with sealed systems where there is a need to retain the traditional hot water storage and central heating systems.

The above is quoted from the glow worm website there words not mine

[Dave Plowman (News)]

So all combis have an integral pressure vessel and integral pump?

[Paulukd]

This doesn't mean that system boilers are only meant to be used in systems with pressurised hot water storage.

As mentioned before, a system boiler is just a regular sealed system boiler with the inclusion of a pressure vessel, pump, and a pressure release value already plumbed and wired within the casing of the boiler.

This is mainly just to make installation into a new sealed system, or an existing open system thats being converted to a sealed system, simpler, quicker and cheaper.

The main disadvantage is that you cant then choose the size of pump and pressure vessel to suit a non typical system, and the case of the boiler is typically a fair bit bigger.

[Dave]

Sorry Alex but that's not correct. System boilers are normally for pressurised heating systems, the type of DHW cylinder is irrelevant providing it's indirect.

[Doctor Evil]

Reflects sales volumes. 99% of combi's are systems boilers with a water section added. 60-70% of all boilers sold (1 million a year) are combi's, so competition is hard and prices are driven down. It is sometimes cheaper to buy a combi and not use the water section than buy an equivalent power system boiler. I a few contractors who do this.

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[Christian McArdle]

No. I have a 3 zone + DHW system running from the Greenstar 28HE and it runs just fine. Zones are upstairs/downstairs/kitchen/DHW. I intend to add a couple more zones. I do have an automatic bypass as well, though, which should reduce noise when running a low load.

Christian.

[Christian McArdle]

I'm afraid you have misunderstood. This quote simply states that it uses a sealed primary system. It says nothing about the design of the hot water cylinder beyond implying that it must be an indirect cylinder. It will work with gravity fed, pumped gravity, mains pressure (i.e. Megaflo) or heat banks.

Christian.