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

[8bit]

Hi, I have a very basic gravity fed system powered by an oil boiler. The bathroom rad is on the hot water loop and has just started leaking at the seam.
It has 22mm pipe feeding it and 3/4" inlets on the rad. Am I wise to replace like for like? Both the old valves are seized and knackered so will need replacing at the same time too.

 

[8bit]

I've recently had success with these on a different part of the system so although expensive they look like they'll be a straight swap.

Belmont 97CPWH Angle Wheel Handle Radiator Valve Chrome Plated - Colglo

www.colglo.co.uk

 

[oldbuffer]

1. It's not strictly a 3/4 inlet to the radiator.
2. The radiator has tail. The part going onto the radiator is 1/2" BSP male thread, as applies to the vast majority of radiators. The part to which the valve attaches is what is known as a union connection. This is indeed threaded 3/4" BSP.
3. The new valves will come with new tails. These tails are likely to have 1/2" BSP threads to screw into the radiator, but plain 15 mm tubes (chrome plated) on the valve side for compression fitting.
4. You can get valves with union fittings and they will come with 1/2" x 3/4" tails, but the TRV valves of this type tend to be a good bit more expensive than compression fitting ones.
5. The radiator looks as if is probably an imperial size. Myson do a range of imperial radiators, but they are more expensive that metric ones.
6. You may well have to make some minor pipework modifications fitting a new radiator, both for end to distances and distance from the walls.
7. My advice would be to:
7.1 Go with a roughly equivalent metric sized radiator. Go for slightly narrower if you can and use extender(s). If not, alter the pipework.
7.2 Make sure the radiator is piped in parallel with the hot water cylinder primary coil. If it is, fit a TRV to the flow connection. (The one which heats up first). If its piped in series with the cylinder coil, don't fit a TRV and make sure both valves are always at least partially open.
7.3 Go for a type 21 (finned one side) or type 22 (two panels with fins in between). You can always turn them down if it gets too hot, but its a bit of future proofing if you eventually go the heat pump route.

 

[8bit]

Thanks, the thread that goes into the rad is about 26mm dia. IS that definitely 1/2"? I guess it doesn't matter if i'm changing the radiator my concern was more do i need a 22mm valve on this for flow or could you step down to 15mm to get a standard valve to fit. I'm assuming it must have been plumbed with bigger pipe for a reason way back when.

 

[oldbuffer]

1. The outside diameter of a 1/2" BSP thread is around 21 mm. That of a 3/4 BSP thread just under 26.5 mm.
2. However, without removing the tails I can't see how you measure the thread which goes into the radiator. This thread is almost certainly 1/2" BSP. The 3/4" BSP thread is on the valve, and the nut captive on the non-radiator end of the tail screws onto it.
3. The flow into / out of the radiator is governed by the narrowest piece of pipework. This is likely to be the radiator tails.
4. I suspect you don't need 22 mm pipe (if that is what it is), 15 mm would be fine.

 

[8bit]

Its definitely 3/4 then, there is one thread visible at the edge of the rad which i measured with a set of calipers.

 

[fixitflav]

Its definitely 3/4 then, there is one thread visible at the edge of the rad which i measured with a set of calipers.

How about a photo or 2?

 

[8bit]

Here you go

 

[Madrab]

It won't matter, the new rad you get will certainly have a 1/2" tapping to take a 1/2" tail, it's the supply pipe you need to watch. If it is 22mm then that's fine but if it 3/4" then that's when the fun starts and what valves will fit. You also won't get a flat panel, it'll be a type11/K1 (metric) that has 1 set of fins so then it's down to how far off the wall it sits and what the pipe centres are.

What is the length of the rad?

 

[8bit]

Its a 600mm x 600mm rad and wall to centre of pipe is 54mm. The feed pipe is 21.7mm give or take(cheap calipers). I've come across a mix of imperial and 22mm in the house already.

 

[Madrab]

If it's a 600mm rad then you're lucky, those old single panels all tended to be imperial @ 24", that being said it's probably the closest imperial to a metric size you would happen to get as 24" is just a smidging over 600mm.

So now it's just about getting 22mm valves with 1/2" tails and then getting the old valves and nuts off the pipe, cleaning up the pipe and making sure it's not overly marked/damaged. Probably need a wrap tape on the olive as a belt'n'braces so get some gas tape as it's thicker and gives a little more wiggle room.

 

[fixitflav]

Its a 600mm x 600mm rad and wall to centre of pipe is 54mm. The feed pipe is 21.7mm give or take(cheap calipers). I've come across a mix of imperial and 22mm in the house already.

The pipe wouldn't be steel by any chance? OD of 1/2" NB pipe is 0.8442 = 21.44mm

 

[8bit]

Thanks for the advise guys, its definitely copper just a combination of crusty paint and a rubbish caliper not giving an exact measurement.

I did see this radiator advertising rads with 3/4 inlets - https://www.rubberduckbathrooms.co.uk/600-x-600-double-panel-type-21-radiator-3712btu

I know i can get the 22mm valve with 3/4 tails linked a few posts up but not sure if i can get one with 1/2" tails. Will have a look about.

 

[Madrab]

I did see this radiator advertising rads with 3/4 inlets

Hmmm, I'd make sure of that, looking at the pics they use standard blanks and vent plugs, which would be 1/2" BSP. The standard for rads these days is 1/2" not 3/4", only some of the old rads were 3/4".

That and the TRV's/valves they show for it are all definitely 1/2" bsp, ergo the number 15 on the valve (15mm)



I'm not saying it isn't I'd just want to check first.

 

[8bit]

Agreed i was going to call and check first as it seems odd. Ta.