Pre plumbed Unvented cylinders with pumps on

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Hi

Can anyone tell me why unvented cylinders come with pumps on? When system boilers come with the pump integral?

Thanks
 
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Thanks for reply but was looking for more of a technical answer,

So do all system boilers come with pumps integral?

Unvented cylinders are mains fed so must be installed with system boiler.

Ive seen some unvented cylinders installed with pumps fitted, i was just wondering what happens to the pump on the boiler that comes integral to the boiler?

Or can you buy system boilers without the pump fitted?

Thanks
 
My unvented cylinder didn't come with a pump and my system boiler doesn't have a pump either but I do have an external pump that pumps the central heating and the indirect hot water. I dont really understand what you are getting at here.
 
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Thanks

So the answer is you can buy system boilers without the pumps integral

Thanks
 
Thanks

So the answer is you can buy system boilers without the pumps integral

Thanks
No, then it wouldn't be a system boiler. A system boiler has in-built pump and expansion vessl. A heat-only boiler doesn't, it needs an external pump and either a F/E tank or a pressurised expansion vessel, depending on preference. Any of them can feed the primary coil of a HW cylinder, vented or unvented.
One of my sons has a heat-only boiler (Glowworm) with external expansion vessel, feeding a pressurised HW cylinder.
 
Good info. So mine is a heat only boiler feeding an unvented HW cylinder. The heating loop is also pressurised via an expansion vessel. Cheers.
 
That makes sense, so when people convert from gravity fed to mains they can keep their conventional boiler as opposed to ripping out and fitting a new system boiler

Just re using existing pump and installing pressure vessel

Thanks
 
That makes sense, so when people convert from gravity fed to mains they can keep their conventional boiler as opposed to ripping out and fitting a new system boiler

Just re using existing pump and installing pressure vessel

Thanks

Correct which is exactly what I did. I had a pressure vessel put in to pressurise my heating system so that I could also remove the header tank in the loft etc (as well as the cold water tank). My unvented cylinder is pressurised of course but mine uses an internal expansion vessel to achieve this - some dont have this and need an external one to be fitted.
 
Excellent, ive learnt something

You must have a megaflo as they have the pattend internal expansion vessel
 
That makes sense, so when people convert from gravity fed to mains they can keep their conventional boiler as opposed to ripping out and fitting a new system boiler

Just re using existing pump and installing pressure vessel

Thanks
Not always, some boilers can be adapted some cant, if you convert from open vent to sealed, the boiler needs over heat and loss of pressure sensors of some kind, the external expansion vessel and pressure releif kit must also be installed, a system boiler has all these inbuilt, a heat only boiler doesnt
 
Excellent, ive learnt something

You must have a megaflo as they have the pattend internal expansion vessel

Mine is not a Megaflow and it has an internal expansion vessel :) and yes, you need to check that your current boiler can be pressurised if indeed you want to pressurise your heating circuit. You can still have a unvented cylinder in either case but you must have adequate mains cold water pressure to run it.
 
And just to add that the larger system boilers come with expansion vessels and pumps that are far too undersized to be of any use.
Far better to have a separate pump/vessel/safety valve/gauge/loop that can be properly sized....and you're not tied to extortionate manufacturers spares prices when they fail.
 
Excellent, ive learnt something

You must have a megaflo as they have the pattend internal expansion vessel
There are at least 3 brands I can think of who offer the floating baffle internal expansion system. I'm not sure any of them have made it work properly - generally more hassle than it's worth
 
That makes sense, so when people convert from gravity fed to mains they can keep their conventional boiler as opposed to ripping out and fitting a new system boiler

Just re using existing pump and installing pressure vessel

Thanks
I think it's been covered, but to recap - you can have a gravity-fed or unvented HW cylinder, with a system boiler, or heat-only boiler, in any combination. I believe system boilers always come with in-built expansion vessel, heat-only can be set up for gravity via F/E tank or pressurised with separate expansion vessel. There's pros and cons for each, starting from scratch it's probably a toss-up, but I wouldn't take out an existing F/E tank and go pressurised. If you do, you need to check the boiler is OK for the higher pressure, and there might be a bigger risk of pipework leaking. Also as ianmcd said, you need to add a pressure relief valve and a pressure switch to cut out on low pressure.
 

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