Can I have a new combi boiler and keep my hot water cylinder

[JohnD]

- and you can't have weather compensation.

why not? All the Viessmanns take it now, even (I hear) the latest 100 Compact. And if you are using a combi with a cylinder on a Y plan, why not?

The cylinder allows you to fill a bath faster than a combi could deliver, or to have a Power Shower, again, with more flow than a combi could deliver

though personally I would prefer the shower on the Combi hw not the cylinder, as it won't run out of hot water

 

[doitall]

Putting in a combi plus a cylinder seems like overkill to me - and you can't have weather compensation.

Just have a system boiler plus cyl, or the floor standing storage combi - which is really a system boiler and unvented cyl combined.

A combi serving the kitchen area with a cylinder serving the bathrooms also gives you immersion back-up if needed.

A combi is like putting all your eggs in one basket, not a good idea when a family is in occupation.

It also take some of the strain of a low water supply.

 

[gas112]

Also considering combi`s have more in them they tend to be cheaper to buy than a system boiler of the same output

 

[kevplumb]

also has the advantage that if somebody turns a tap on in the kitchen you dont get frozen/scalded in the shower

have done a few and custs where very pleased

 

[ajrobb]

A combi might give a better shower than a vented cylinder (unless pumped) but the cylinder can fill a bath quicker.

http://www.gasapplianceguide.co.uk/Mains_Pressure_Hot_Water_Systems.htm

Unvented cylinders run at mains water pressure (regulated down to 3 bar) and apparently require annual inspection. Alternatively, you can have a hybrid 'vented mains pressure' system that uses a heat exchanger in a vented cylinder to heat mains water on demand.

When you draw water from a cylinder (vented or unvented), it must be at least 60°C to prevent disease. There are about 60 deaths per year in Britain due to getting into hot baths. I suspect that demand heating can be at a much safer 45°C.

 

[mickyg]

blimey, so many options! crikey all the op needs is a replacement boiler, nothing else needs doing, already got a cylinder in place.... Lets face it if you went in to quote in an average house and they've got a cylinder and want to keep it and got rubbish mains pressure all your gonna do is quote to replace the boiler and upgrade the controls. So why recommend something different cos your on a forum? come on ppl be realistic! Keep it simple

 

[blondebier]

Thanks for all the suggestions guys.

I probably forgot to say that I'd like to get rid of the cold water storage tank in the loft. Does that change things at all?

In an ideal world I'd like to lose the storage tank in the loft.
Have mains pressure cold water to all the taps.
Deliver as close to mains pressure hot water to the hot taps.
Drive our central heating system.
Have a new hot water cylinder in the airing cupboard with an immersion heater as a backup.

If I go down the combi route and get that to supply the kitchen only, what sort of cylinder should I get? Would I need a pump to supply the shower and taps in the bathroom?

I didn't think this would get so complicated...

 

[blondebier]

Thanks MickyG.

Simple is good! At least simple enough for me to understand how it works...

I had a look at the GasApplicanceGuide link that AJRobb(thank you) posted and it sounds like a vented mains pressure system is probably what I'm after.

So in simpleton's terms I could get a system boiler and a vented cylinder and lose the storage tank in the loft.

This would give me mains hot water to all my taps and I'd have hot water backup via the immersion heater in the cylinder.

Simple or flawed?

 

[ajrobb]

So in simpleton's terms I could get a system boiler and a vented cylinder and lose the storage tank in the loft.

I think a vented cylinder requires a cold storage tank. The storage tank could be sited below the loft insulation in the airing cupboard.

Although not your preferred option; if you lose the storage tank then a cylinder will have to be unvented. Unvented cylinders are expensive pressure vessels and require regular maintenance.

 

[blondebier]

I think a vented cylinder requires a cold storage tank. The storage tank could be sited below the loft insulation in the airing cupboard.

That link you posted seemed to indicate otherwise though...

I can see how you would need it in a gravity fed system. But is it really necessary in a vented mains pressure system?

I am well and truly confused now.

 

[Agile]

A vented system is a gravity fed system!

Tony

 

[blondebier]

A vented system is gravity fed system!

I thought so too, but the link that AJRobb posted to the gas appliance guide suggests otherwise...!

Under the "Vented mains pressure system" table it states : No loft tanks - space saving

 

[ajstoneservices]

A vented system is gravity fed system!

I thought so too, but the link that AJRobb posted to the gas appliance guide suggests otherwise...!

Under the "Vented mains pressure system" table it states : No loft tanks - space saving

You're getting confused, take another look

 

[blondebier]

You're getting confused, take another look

This is what it says...

In a vented system, heat is imparted to the incoming mains water by means of a secondary heat exchanger within the vessel. Water in the vessel is used rather like a battery for heat - a Thermal Store. The incoming mains water passes through it's heat exchanger within the vessel drawing heat from the store. The Thermal Store temperature is maintained in the usual way - either Directly with electrical heaters, or Indirectly by your boiler.

Because the water within the Thermal Store does not need to be under pressure (as with an unvented system) it is vented to atmosphere. The body of water within the Thermal Store is used purely as a medium for storing and imparting heat to the secondary exchanger.

That sounds fairly clear to me. It doesn't state or even imply that it is a gravity fed system that utilises a storage tank in the loft.

 

[ajstoneservices]

If you have a gravity fed system then you need a cistern in in the roof space to feed your vented cylinder.
If you have a thermal store you may need an feed and expansion tank in the roof space. if you have a Combination thermal store you will not need an f&e or a cistern.