How do I drain a radiator that comes on with the hot water?

[andrewj100]

Hi, this is my first post!

I've got a very old boiler it's gas and installed in the dining room fire place.
Of the radiators upstairs two, bathroom and small bedroom, get hot when the boiler is heating water for the water tank.
Other radiators in the house only get hot when the the central heating is activated.
I've done some hunting around on the Internet and it looks like these are some sort of protection to prevent the boiler actually boiling the hot water system, probably from the pre-electronic control days and possibly a throw back from a solid fuel heating system.

The radiator valve on the radiator in the small bedroom is weeping and needs replacing (I'll probably do the rad as well) but I'm not sure how to drain this part of the system down. I obviously cant take the valve off with water still behind it waiting to come out.

The drain point next to the boiler has seized so when I gutted my kitchen and replaced the radiator in there I added in a drain point next to the kitchen radiator.
My question is, if I drain from this point on the radiator system will I also drain the hot water circuit that's feeding the small bedroom and bathroom radiators (and presumably the hot water tank)?

 

[seco services]

just isolate the feed to the loft tank and drain from kitchen draincock.

turn your programmer so it don't call for any heat while its drained.

 

[bengasman]

Personally, I would turn the electricity to the boiler off at the spur, and trun the gas off as well; I am a coward.
The only things that are separated are the water that comes out of the (hot) tap, and the the water that goes through the boiler; you drain the rads and the cylinder together.
Make sure you turn the correct tank off; you should have a big one and a small one, the small one feeds the boiler.

 

[andrewj100]

I can turn the boiler to OFF which stops it starting up but leaves the pilot light going (it's a pain to relight) and also switch the controller to OFF/OFF which will also stop it starting.

Thanks for everyones help on this.

bengasman:
I only have one tank in the loft with two feeds off it, one for the upstairs toilet and bath, the other leaves the tank and splits further down to go either to the heating system or hot water tank.
This has made me nervous of ever using rust inhibitor as I really don't fancy water expansion pushing rust inhibitor back up and contaminating the feed to the hot water tap circuit or, if it pushes up far enough, to the upstairs cold water circuit.
The only way I could probably get it in to the system would be down stream, directly into a radiator.... that would be fun.
I probably could split all this out to two tanks but the intention is to get a combi boiler in at some point in the future which would do away with the lot!

 

[bengasman]

I have seen systems with only one tank, but they are very rare. If this is really a one tank system (meaning the tank is not internally separated, I trust you can count to two) adding inhibitor would be pointless as it would soon be so diluted as to loose its working.

You will soon find out; if the draincock stops letting water out, but you can still run the bath tap, most likely the tank has an internal separation.

 

[seco services]

sounds like you have a primatic cylinder.

you won't be useing inhibitor if its a primatic

 

[tamz]

Turn off system at programmer or spur if you feel safer, the boiler can't light without electric so no need to turn off gas or relight pilot.
If you have a primatic cylinder the flow and return to the cylinder will not have a feed or expansion pipe off them. They just go straight into the cylinder, no tees. The heating is fed through the cylinder with the water being separated by an air bubble (like a kind of upside down bucket inside it).
If you are not sure what to turn off just open the drain valve first then go into loft and turn off stopcock on tank that is filling (or the hot water feed if you know where it is).
Also open your hot taps and cylinder drain if you like. It will drain faster (all comes from same place).
Filling is no more difficult than any other system.
Close drain valve(s)
Turn water on.
Fill hot water side first.
Fill heating.
Don't add inhibitor The air break can separate in the cylinder and mix the water.

The problem with upstairs radiators heating can be fixed by adding an anti gravity valve or by altering the flow pipe to tee in below the boiler (under the floor or as low as you can get it)

 

[andrewj100]

Looks like I have more investigation to do then!

The tank in the loft has no separator in it, I was up there with a tourch when I did my kitchen.
Once the ballcock was tied up the central heating and hot water had to be drained seperately, after emptying all the radiators the water tank was still full of warm water.

There is definately a "tee" down stream of the loft tank.
A large diameter pipe runs into the airing cupboard and as it comes in through the celing it splits into two, one goes into the top of the copper water tank, the other runs down the wall to the dining room below that has the boiler. Is this typical of a primatic cylinder?

And, this may sound like a stupid question, how do you know you still have the required air bubble in a primatic cylinder?

 

[doitall]

If you look on the side of the cylinder, above where the heating pipes connect to it, it will be stamped Primatic in the copper.

 

[andrewj100]

I've had a look around the cylinder, it has a sticker on saying "uni-cyl, fit as a direct cylinder" it's made by Uttley Ingham and co ltd, I've had a hunt on the internet and cant find anything about it, I cant see Primatic stamped on it.
I'm sure someone is going to make a comments like "you need to get that to a museum".

 

[kevplumb]

direct cylinder on a gas boiler

 

[doitall]

direct cylinder on a gas boiler

No, it's a uni-cylinder, which I think was the same as a Primatic.

 

[kevplumb]

before my time i'm only a young un

you should remember them well

check your e mail

 

[doitall]

before my time i'm only a young un

you should remember them well

check your e mail

WOuld that be the first or another.

 

[kevplumb]

" i am appalled "