Vented Hot Water with Unvented Central Heating

[greenmachine]

Hi All,

Thanks in advance for reading:

I currently have a gravity fed indirect central heating/hot water system. I have a very old primatic vented hot water cylinder in the loft with cold water storage header on top. The boiler is relatively new - a Worcester Bosch Greenstar 18Ri. There is also a 3 way valve and pump under the bathroom floor which is tiled.

As the cylinder has recently started leaking, and coupled with the fact that I can't use inhibitor in the system due to the potential of mixing the CH and DHW, I have decided that now is the time to get it replaced. After doing some research, I was under the impression that the easiest thing to do would be to do a straight swap with a new, same-sized (800 x 450mm) vented cylinder. Not being a plumbing expert, I called in my local central heating engineer. He has now recommended that rather than just doing a like for like swap and leaving the system fully vented, that it would be useful to keep the hot water vented, but to somehow pressurize the central heating system. He says that closing the central heating system will stop air getting into the system, corrosion, sludge, knocking etc. Apparently the the current boiler, pump system etc will support this as all that is needed is some kind of filling loop (I don't know the exact details) to fill and keep the central heating system unvented. There is also hardly any extra cost (apart from filling loop equipment etc).

Having done some more research I can't really find any mention of this type of installation. I have several questions:

Is this feasible to do?
As I don't have a combi-boiler, is my current boiler suited to this type of system?
Will my pump/radiators etc cope with the extra pressure? I don't want to risk leaks (especially ones under tiled and decorated areas).
Is it worth doing?

Thanks
Martin

 

[mountainman]

So what you are really saying Martin is that you have asked a heating engineer to give you his advice (was it free or chargeable) but you don't trust him.
As a second option you thought you might trawl the Internet to find opinions to reinforce your doubts.
Why not just get a couple more free quotes from local engineers and see what they recommend.

 

[diamondgas]

:welcome: to the forum

You telling us that you have a condensing boiler fitted to a gravity primatic cylinder greenmachine..? That's too funny!!! LOL

EDIT: It is also indirect and has a valve and pump under the bathroom floor Tiled ..........

Is this a wind-up?

 

[stevetheplumber]

i very much doubt the cylinder is primatic its a comination cylinder with the tank on top often called a fortic the primatics filled the heating from the cws and ive never seen one with a tank on top a picture would help
closing the heating system isnt a problem as most system now are sealed you will need more than a filling loop to do it
any sytem with a primatic would have so much rubbish in it the greenstar would have died in a week

 

[diamondgas]

I've had to re-read your post a few times Martin ... Personally I'd want the pipes under the tiled floor accessible or moved somewhere accessible! They're going to go wrong at some time!

It also sounds like you're describing a system that has issues with 'pumping over'? A sealed system will stop this happening but does bring with it potential problems ..

If you've got 'knocking' you may benefit from a flush too!

Get yourself some quotes martin! I think your system needs a real life visit to give you best advice unless you can post some pictures up here to help us see what you're talking about IMHO

 

[greenmachine]

Thanks for the replies. Maybe my information on it being a primatic cylinder was somewhat wide off the mark judging by the incredulous replies! I've attached some photos of the offending cylinder.



mountainman - the main reason I have asked the question on here was to get any opinions from a large a population of experts. I had a central heating engineer around today, another chap is coming tomorrow and in the meantime thought I'd ask the question on here. I like to be sure that the solution I am going to be paying for is ultimately the right one in the long term. I also like to understand (as much as possible) about the solution. Its nothing to do with not trusting anyone.

It also sounds like you're describing a system that has issues with 'pumping over'?

diamondgas - I'm not sure what you mean by pumping over. Apart from the leaking cylinder the system seems to work well at the moment.

Thanks
Martin

 

[stevetheplumber]

blimey that is an old beast i realy couldnt say with any certanty its not primatic seeing the size of the tank on top
does the tank on top supply cold down service as well ? have you any other tanks where in the country are you ?
'i d love you to say morth london but cant see it

 

[arran197]

Going back to your original question, you can change to a sealer system, but there are things to think about before doing it.

Firstly you will need more than just a filling loop. You will also have to have a pressure gauge, an expansion vessel suitable for the size of the system and most importantly, a pressure relief valve which will have to be piped to the outside somewhere.

Secondly, if you do change to a sealed system, be prepared for leaks. You might need to factor in the cost of repairing any leaks that might crop up due to the increased pressure in the system.

Thirdly, if the boiler is a Greenstar Ri, you CAN run these on a sealed system, in fact I think Worcester would recommend it.

 

[greenmachine]

does the tank on top supply cold down service as well ? have you any other tanks where in the country are you ?

Steve, as far as I know the cold tank on top just supplies the hot water cylinder and central heating. All taps are mains fed. Is this what you mean?

I'm up in the good old north west, Oldham to be accurate. I believe most of the houses on my estate had this type of cylinder fitted originally, the houses were built some time in the late 60's/early 70's.

 

[chris watkins]

Hi Greenmachine
If you have to replace the cylinder & as you say cold is direct from the main with hot from the tank fed cylinder in the loft you will have unequal pressures between the two & most likely have problems with mixer taps &/or showers, I know it may be a bit extra cost but nows the time to look at a solution I would think about replacing the cylinder with an invent one which would mean that all the water in the house would be from the mains & so equal pressure. This does depend on where your mains will supply both a plumber (unvented ticket, G3) will need to check pressure & flow rates but most OK. The cost difference between indirect copper cylinders & stainless steel un-vented units has closed dramatically & they often carry a 10 - 25 or even life time warrantee on the tanks. The heating would be OK if it converted to a sealed one the trick, as far as possible leaks are concerned, is not to pressurise it more than what the old one was i.e. if 2 story house with old F&E in loft = then around 0.7 - 1 Bar maximum. (Head of water in Metres x 0.1Bar).