Drain system add trv's?

6 Jan 2010
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United Kingdom
Hi all,

Im looking to add 3 TRV's to my system i have 7 rads in total, ive looked at the Faq's about this subject just looking for more specific info for my sytem my main issues are:
Do i need to drain dow the system to add trv"s or can i lock off the flow to the rad drain that rad and fit the trv to the return side?
If i do need to drain down my system how do i go about it also how do i re-fill the system.
I live in a bungalow, my system has 7 rads ruuning with a worcester bosch boiler.
Any info greatfully recieved
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If your boiler is a combi then its dead easy, as once the system is depressurised you won't get much water escaping.
If you have stored hot water, it means a drain down.
Use quality TRV's;
Put them on the flow side to the radiators;
Don't forget the inhibitor when you refill!
John :)
If you have stored hot water, you could bung the vent pipe and feed/outlet from the F&E tank, to create a vacuum. Saves drain down, and the arse-ache air locks that these systems are prone to.
Hi its a combi boiler so no stored hot water, feeder etc. how do i depressurise the system?
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Open a draining point, or open bleed valve on a radiator and let excess water squirt out. In fact, once you remove the tail from a rad valve, and let the excess water out, it will depressurise.
ok so i should just turn off the boiler and drain the water from the rad via valve on the flow side this will allow the excess in the pipes to escape and depressurise? when i come to refill the system my boiler has a key i insert and turn a knob fill/add pressure is there anything i should do to avoid airlocks?

You shouldn't really have air lock woes with a combi. Sometimes though, its better to fill the system slowly, rather than opening the taps to fill system at full bore.
would you advice draining all 3 rads changing each locksheild to a trv then refill the system. do i need each bleed valve open on then rads whilst filling?

If you do one rad at a time you can check for leaks as you go - and add the inhibitor to the last one.
John :)
can i lock off the flow to the rad drain that rad and fit the trv to the return side?
Unfortunately water does not flow in one direction. Shutting the flow will stop water entering the rad from that end, but it can still flow backwards into the rad through the return. As soon as you start undoing the return you will get the system draining through that valve.
Why on earth would you want to mess about with your heating in the middle of an ice age. If it ain't broke leave it till it's warmer.

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