22mm pipe and 3/4" rad on Hot water side of old gravity system

[8bit]

Last question! The heating side of the system is refilled via a primatic hot water cylinder, will the hot water side of things refill in the same way?

 

[Madrab]

via a primatic hot water cylinder

Oh, right, be very very careful - if the system drains down out of the cylinder and it has a primatic cylinder, you probably know that you need to very carefully about how to re-charge the cylinder.

They do self prime via the Cold Water cistern (CWSC) but you need to be very careful to ensure the bubble is formed again otherwise the water can mix, you can't use inhibitor either, just in case.

Every considered replacing the cylinder? Might be a good idea.

 

[8bit]

Hmmm, thats good to know, i had a plumber add a couple of radiators recently and he refilled with inhibitor in the system!
The trouble i have is the roof space is VERY shallow, at a guess about 500mm at the highest point so the main cold water tank sits above the cylinder in the airing cupboard.
I could probably squeeze a 50l tank up in the loft but working up there would be a pain in the arse(but doable). The joys of a weird 60's house! I'm assuming worst case if they did mix its not a life ans death situation as we're not inclined to drinking the hot water.
We plan on doing a bit of remodeling work in about 5 years so its likely the system will be pulled out then so for now i'm just trying to make it last.

 

[Madrab]

i had a plumber add a couple of radiators recently and he refilled with inhibitor in the system!

Not good, you don't want inhibitor into any water that you may use personally, if it did mix then you can inhibitor into your eyes, mouth etc just by washing, I'm sorry to say but that needs sorted out sooner rather than later, did he not know it was a primatic cylinder? Not life or death no, but very undesirable.

You could just replace your current cylinder for a norm vented cylinder using what you have just now and nothing would be that different, it would just mean it would use a coil and there wouldn't be any concerns.
If the future, if your mains allows, then you could shift to a mains driven HW system.

 

[8bit]

Would i not need a fill/expansion tank in the loft? It sounds like thus might be the way to go tbh.
I'll get the plumber back to drain down and refill the system in the meantime.
I'm also still trying to get my head around the draining/refilling of this bathroom rad thats on the hot water gravity side of the boiler and how its separated from the CH side of things.

 

[8bit]

Having had a little read up it sounds like a small 18l (ish) tank might be sufficient in the loft? I recon i could get one of them up there along with the associated pipework easy enough.

 

[Madrab]

Would i not need a fill/expansion tank in the loft?

Yes, unless you sealed the system you have, what boiler etc do you have, I presume it's an oldy but goldy if you have gravity HW. The F@E tank could possibly be located in the cupboard too as long as it's above the level of the highest CH pipework, nope, it doesn't need to be large.

The gravity HW will be the primary circuit from the boiler on big fat pipes (28mm/1") that heat the HW cylinder, from the sounds of it. Therefore that rad may have been added to that circuit as a heat sink. So in essence you have a gravity HW and Pumped CH. If that's the case then that is the one that when drained could pull the bubble from the cylinder, mixing the system water with the HW.

Time to upgrade you system methinks

 

[8bit]

Thats exactly what it is, the boiler is an old Trianco TRO 12/14 which must be coming up for 40 years old. The house hadn't been lived in for 5 years before us and it fired straight up.
I'm thinking an oil combi might be the answer when the time comes to free up some space in the bathroom. The airing cupboard is already rammed full so the f&e will have to be in the loft.
Thanks for all of the advise.

 

[fixitflav]

Would i not need a fill/expansion tank in the loft? It sounds like thus might be the way to go tbh.
I'll get the plumber back to drain down and refill the system in the meantime.
I'm also still trying to get my head around the draining/refilling of this bathroom rad thats on the hot water gravity side of the boiler and how its separated from the CH side of things.

If you're thinking of replacing your Primatic with a fully indirect cylinder (a good idea in the circs!) it's worth converting to a Honeywell C-plan as on attachment. Needs a 28mm motorised valve but you'll need to drain the system down and modify the cylinder primary side anyway. Much more flexible and potentially more economical than your current set-up.
18l F/E tank should be fine.

Edit - and Merry Christmas!