Is a System Boiler better in use than a regular Boiler?

[steveatesh]

I have to replace my Boiler, gas fired, regular boiler powering an unvented hot water and vented central heating system.

I've gone through the "which boiler" thing and decided on a make but one plumber has quoted for a "system" boiler to make the whole heating and HW unvented, the other has quoted for straight replacement regular boiler.

The system boiler is just under £500 more to install, but if I was to get any actual benefits from a system boiler over a regular boiler then I can weight that off.

I know the mechanics of the differences between the two types of system but can't get a definitive answer to the question is one better than the other in daily use? In other words, is a "system" boiler and totally unvented HW/heating system inherently better than a Regular Boiler with Unvented HW but vented heating (as it is now).

i.e. hotter radiators? Heats up quicker if so how much quicker? reliability? anything else?

Or will I not notice any difference in reality?

[mikeiow]

I suspect this is a bit of a Nikon v Canon question.....*most* plumber would work with (& therefore be more familiar with?) 'regular' boilers.
We moved our boiler to the attic and went "unvented mains pressure system boiler" back in 2008, and it has worked a treat for us. Gas central heating all good, hot water pretty well on demand, & indeed because the tank heats the water coil up, you get mains pressure hot water on demand (I think we have a 250l tank in the airing cupboard and no more cold tank in the loft).
So my vote would be yes, system boiler is great. but equally I would get a plumber who is familiar with them to install it!

[Neil - YVM]

steveatesh said:

I have to replace my Boiler, gas fired, regular boiler powering an unvented hot water and vented central heating system.

I've gone through the "which boiler" thing and decided on a make but one plumber has quoted for a "system" boiler to make the whole heating and HW unvented, the other has quoted for straight replacement regular boiler.

The system boiler is just under £500 more to install, but if I was to get any actual benefits from a system boiler over a regular boiler then I can weight that off.

I know the mechanics of the differences between the two types of system but can't get a definitive answer to the question is one better than the other in daily use? In other words, is a "system" boiler and totally unvented HW/heating system inherently better than a Regular Boiler with Unvented HW but vented heating (as it is now).

i.e. hotter radiators? Heats up quicker if so how much quicker? reliability? anything else?

Or will I not notice any difference in reality?

The big difference is the pressure of the hot water.

A pressured system, ie with a system boiler will deliver hot water at close to mains pressure, so giving much better showers, filling the bath quicker etc.

For £500 difference I would go for that every time.

[Gingerbread Man]

Neil - YVM said:

steveatesh said:

I have to replace my Boiler, gas fired, regular boiler powering an unvented hot water and vented central heating system.

I've gone through the "which boiler" thing and decided on a make but one plumber has quoted for a "system" boiler to make the whole heating and HW unvented, the other has quoted for straight replacement regular boiler.

The system boiler is just under £500 more to install, but if I was to get any actual benefits from a system boiler over a regular boiler then I can weight that off.

I know the mechanics of the differences between the two types of system but can't get a definitive answer to the question is one better than the other in daily use? In other words, is a "system" boiler and totally unvented HW/heating system inherently better than a Regular Boiler with Unvented HW but vented heating (as it is now).

i.e. hotter radiators? Heats up quicker if so how much quicker? reliability? anything else?

Or will I not notice any difference in reality?

The big difference is the pressure of the hot water.

A pressured system, ie with a system boiler will deliver hot water at close to mains pressure, so giving much better showers, filling the bath quicker etc.

For £500 difference I would go for that every time.

He already has an unvented cylinder, so the hot water aspect won't change.

Central heating systems tend to work better pressurised. You loose a tank, or the remaining tank in your case out of your loft. Systems bleed better and tend to run nicer. A correctly set up system should pull in air, but an unvented system removes this chance.
If you've a leak at all, it'll show once pressurised. Also any water that might leak out, won't be replenished, so if if you ever had a burst or similar it would minimise damage.

[Neil - YVM]

Gingerbread Man said:

Neil - YVM said:

steveatesh said:

I have to replace my Boiler, gas fired, regular boiler powering an unvented hot water and vented central heating system.

I've gone through the "which boiler" thing and decided on a make but one plumber has quoted for a "system" boiler to make the whole heating and HW unvented, the other has quoted for straight replacement regular boiler.

The system boiler is just under £500 more to install, but if I was to get any actual benefits from a system boiler over a regular boiler then I can weight that off.

I know the mechanics of the differences between the two types of system but can't get a definitive answer to the question is one better than the other in daily use? In other words, is a "system" boiler and totally unvented HW/heating system inherently better than a Regular Boiler with Unvented HW but vented heating (as it is now).

i.e. hotter radiators? Heats up quicker if so how much quicker? reliability? anything else?

Or will I not notice any difference in reality?

The big difference is the pressure of the hot water.

A pressured system, ie with a system boiler will deliver hot water at close to mains pressure, so giving much better showers, filling the bath quicker etc.

For £500 difference I would go for that every time.

He already has an unvented cylinder, so the hot water aspect won't change.

Central heating systems tend to work better pressurised. You loose a tank, or the remaining tank in your case out of your loft. Systems bleed better and tend to run nicer. A correctly set up system should pull in air, but an unvented system removes this chance.
If you've a leak at all, it'll show once pressurised. Also any water that might leak out, won't be replenished, so if if you ever had a burst or similar it would minimise damage.

Ooops my mistake, must skim read more accurately.

[silversurfer1]

steveatesh said:

I have to replace my Boiler, gas fired, regular boiler powering an unvented hot water and vented central heating system.

I've gone through the "which boiler" thing and decided on a make but one plumber has quoted for a "system" boiler to make the whole heating and HW unvented, the other has quoted for straight replacement regular boiler.

The system boiler is just under £500 more to install, but if I was to get any actual benefits from a system boiler over a regular boiler then I can weight that off.

I know the mechanics of the differences between the two types of system but can't get a definitive answer to the question is one better than the other in daily use? In other words, is a "system" boiler and totally unvented HW/heating system inherently better than a Regular Boiler with Unvented HW but vented heating (as it is now).

i.e. hotter radiators? Heats up quicker if so how much quicker? reliability? anything else?

Or will I not notice any difference in reality?

You will not notice a difference between a regular and system boiler when in daily use ie heat up times.

With the system boiler you will have to keep an eye on the system pressure and top it up when needed via a filling loop, on a conventional boiler this is done via the feed and expansion tank although With a system boiler your never going to need to unblock a cold feed.

The system boiler will be larger in size than a conventional boiler and will increase the pressure running in the heating system to about 2 bar when hot so that will need some concideration.

You can always pressurize the heating system using a conventional boiler as well by just some pipe work alteration and the addition of a seperate expansion vestal
shouldnt cost 500 more to do so.

What make are you going for ?

ss

[steveatesh]

Thanks all for your replies. Another thought - looking at the schematics of each boiler type obviously there are more parts in the system boiler. Am I right in thinking that if the pump breaks in a system boiler I would have to purchase the manufacturers part i.e. no choice as to the replacement and therefore probably at an inflated price?

The boiler make was between Valiant and WB - I've decided to go for the WB, I know there have been many discussion about that on here!

[Rickyy]

Personally, if space isn't an issue, I'd fit a regular boiler and then pressurise the heating system.

The boiler is simpler, you can fit whatever pump you want and also, you can fit whatever expansion vessel you want. Boiler expansion vessels can be pricey.

[Sheepshanks]

True, but most boilers come with long guarantees now so that'll cover the internal pump. And if you get boiler only breakdown cover it'll be covered too.

My main concern would be pressurising a previously unpressurised system! Mine was mainly done in Hep2O about 20yrs ago and it terrifies me!

[steveatesh]

Sheepshanks said:

True, but most boilers come with long guarantees now so that'll cover the internal pump. And if you get boiler only breakdown cover it'll be covered too.

My main concern would be pressurising a previously unpressurised system! Mine was mainly done in Hep2O about 20yrs ago and it terrifies me!

My system was built in 1997, it's copper piping, I think about 10mm . Never had any leaks up to now but then again never been under pressure!

[rongagin]

I had a WB system boiler installed last year by a WB installer so a 7 year warranty.

[Depthhoar]

Plenty of good sense already. If I were you I'd get a system boiler that will provide unvented (mains-pressure) hot water + central heating as well. That way you'll do away with a header tank in the loft which is prone to freezing up in very cold conditions + can block at random times. If your CH system works OK now it will also work fine with a system boiler (* but see below). Have this set up at home and the system runs at 1 bar pressure.

• Top tip! If you do go for the CH & HW system boiler it would well worth power flushing the CH system to clear the crap out that inevitably gathers in the rads and reduces heating efficiency. A plumber should charge about half a days labour to do this. Many plumbers have a dedicated power flushing machine. Really important that all the rads are banged/tapped to dislodge the magnetite (rust) and the system refilled with an additive something like Fernox corrosion inhibitor.

[Rickyy]

steveatesh said:

Sheepshanks said:

True, but most boilers come with long guarantees now so that'll cover the internal pump. And if you get boiler only breakdown cover it'll be covered too.

My main concern would be pressurising a previously unpressurised system! Mine was mainly done in Hep2O about 20yrs ago and it terrifies me!

My system was built in 1997, it's copper piping, I think about 10mm . Never had any leaks up to now but then again never been under pressure!

I wouldn't worry. The only time I raise concerns about converting an open vented system to a pressurised one, is when there are pipes buried in the screed or very old rads.

[Pheo]

Just to be clear, the choice of system boiler vs regular boiler has nothing to do with unvented vs vented hot water systems.

A regular boiler will use a feed and expansion tank in the loft connected to the heating circulation system to allow for expansion and refill due to loss

A system boiler does not have this tank, but has an internal pressure vessel meaning the system is sealed, and pressure will rise when in use.


I have a regular boiler with an unvented hot water system. I would not have paid an extra £500 just to get rid of a small feed and expansion tank in the loft which is causing me no bother. Additionally, in the past, virtually every other problem I've had with combi-boilers (which have the same expansion vessel) has been with the expansion vessel failing. Whereas our house now has the same F&E tank as when it was built, with no issues. I'm a big fan of reducing the complexity in the system, not increasing it by adding every component to the expensive boiler which requires a gas engineer to fix. If my system isn't filling up, I can sort it myself.

[BERGS2]

Just to resurrect, in light of our current boiler/central heating conundrum:

- we have added a 4 x 10 extension to the side of the house - Three new bedrooms and an additional bathroom upstairs
- We have an unvented system which has a relatively new boiler attached
- The plumber has recommended ripping out the existing 2x vented tanks to fit a single pressurised cylinder (Megaflow - i believe)

My question to the masses is which is the difference between a 'system boiler' and a regular boiler?

we have a worcester 24Ri - he thinks this would be fine to power the cylinder - but not necessarily the rads.

can anyone who's had similar done in the recent-ish offer any sage advise?

is the install of a new megaflow tank necessitating a new 'system' boiler as they are fundamentally different - or is a 24k just under spec for powering the heating of the newly enlarged house?

Cheers

BERGS