changing a rad on an unvented system

[fowler1974]

I need to change a rad to a towel rad in a bathroom on an unvented system (Heatrae Sadia). Unfortunately I can't freeze the pipework so what are the implications of draining the system? Is an airlock a potential problem?

What is the best way of completing the job?

Thanks in advance
G

 

[WDIK]

why would a domestic hot water heater be connected to a radiator

 

[JohnD]

if it is unvented it will not leak much. You do not need to drain it. Close both the rad valves and take off the rad, emptying it into a bowl or tray. Turn it upside down before you carry it away to stop water dripping out.

If you need to remove the rad valves, you can open one, and a small amount of water will come out into your basin. Do whatever you have to by way of changing the valve or altering the pipe. When you have finished, close that valve and do the other one.

As long as you only have one open pipe end, water will not come out in more than a trickle followed by a few drops.

If you open two, on the same rad, it will quite probably be OK, but it is safer to only open one at a time.

Because there is only one open point, air cannot get in to displace water, so it will not come out. This is like the old "invert a glass of water with a beer mat on it" trick.

When you have finished, refill, pressurise and bleed.

 

[fowler1974]

Thanks JohnD very thorough, I'll do exactly that.

G

 

[Goldspoon]

if it is unvented it will not leak much. You do not need to drain it

?

Am I missing something here? The central heating water will be sealed and pressurised to something around 1.5 bar won't it? If he opens a rad valve it's going to come out rather smartish and make a hell of a big puddle...

 

[gavinda]

If you need to remove the rad valves, you can open one, and a small amount of water will come out into your basin. Do whatever you have to by way of changing the valve or altering the pipe. When you have finished, close that valve and do the other one.

As long as you only have one open pipe end, water will not come out in more than a trickle followed by a few drops.

If you open two, on the same rad, it will quite probably be OK, but it is safer to only open one at a time.

Because there is only one open point, air cannot get in to displace water, so it will not come out. This is like the old "invert a glass of water with a beer mat on it" trick.

When you have finished, refill, pressurise and bleed.

change many rads do ya.


OP if i were you i'd relase the pressure through a drain off, there wont be a great deal of water but still this is the sfaer way. as for airlocks, there is still a chance but less than on an open vented system.

 

[JohnD]

I may not have expressed it well

what I had in mind is that the whole 100 lites (or whatever) in the system will not all come out. Once enough has come out to release the pressure, it will slow and almost stop.

You are right about using the drain cock to let the pressure down, this is cleaner than letting it come out of the rad valve or tail.

The first time I used this method myself, I was surprised how well it went.

 

[gavinda]

perhaps the 1st time you did it the pressure was allready low , id expect a sealed system to spray more than a vented system being bunged.

i'd also recommend doing only 1 valve at a time, the less open ends the better chance you have of keeping your airlock.

 

[JohnD]

I did use the drain cock until it stopped flowing, should have remembered that.

I agree about only doing one at a time, but I've had people on here tell me that they do both valves at the same time without probs I'd be too scared.

 

[gavinda]

I've had people on here tell me that they do both valves at the same time without probs I'd be too sensible.

fixed