drain sealed system

8 Oct 2005
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United Kingdom
I have a combi boiler sealed CH system, supplying 10 radiators. I previously fitted a trv to a lounge radiator using a pipe freeze kit. I now want to fit trvs to 8 other radiators, leaving the bathroom one as it is [permanently on for drying towels].

I have located the filling loop and drain tap, and am planning to drain the system so as to fit the trvs this weekend. I have obtained a kit for adding in corrosion inhibitor via radiator bleed valve when I refill the system.

Is there anything I should watch out for?
Should I close the valves on the CH flow and return pipes under the boiler?
What about turning off the boiler completely [including DHW] while working or can I just turn off the heating?

I am getting a bit worried that some websites say do not attempt to drain sealed system with out professional help :confused:

Any advice gratefully received!
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Isolate the boiler electrically first, ie switch off fused spur, take out fuse. I wouldn't touch the isolators on the boiler flow/return.

Empty system via drain, open rad valve bleeds.

The only prob really as i see is fitting the TRVS onto the existing rads/system. :LOL: Sometimes they go ok, sometimes not.

Refill and vent, check for leaks etc

Good luck :D
Cheers mate.
Are you saying that the trvs might not fit? I hadn't thought of that...still I can always put the old valves back on in worst case scenario.
One thing - refill and vent?
Do you mean bleed the air out with the rad bleed valves, or am I being a bit dense here?
Yes vent via bleed on radiators, normally upstairs, but check all as best practice. Beware that when you do vent, that the pressure will on your boiler guage go down, due to air being released, so fill to 1.5-2.0 bar via the fill loop, vent/bleed rads, check guage, refill, vent, check guage, so on.

If you got stairs it will keep you fit :D or get someone to top the pressure as you vent.
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As for fitting the TRVs, it depends on the valve you are replacing, and what pipework and size you have.
Thanks for the advice, gas2air.
All went well.
The drain valve did drain through the valve itself, as well as the hose connector, but an old towel took care of that..
Hardest thing was removing the old olives from the flow pipes.
Now my house is equally warm, upstairs and down! :D

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