CH Drain down

[John Ledger]

I have drained down my (vented) CH system to replace some rads etc. Will the drain down affect the hot water side of things, i.e. is the coil in the copper tank still full of water and able to heat the domestic water. As far as I know I have only drained the CH system (via a drain c*ck on one of the downstairs rads). Or will I be better using the immersion heater for a few days while I am working on the CH?

Cheers

John

[Hugh - Was Invisible]

Assuming that you have one central heating boiler etc for both the hot water and the CH system then the same water heated by the boiler will pass through both systems. You will have to use the immersion heater until the system has been refilled.

Make sure that the boiler cannot fire up or the pump run while the system is drained.

[Roger Mills]

That is correct. The radiators and the coil in the HW cylinder are all part of the *primary* circulation system - so if you have drained the radiators[1] you've no longer got an operational primary circuit.

[1] UNLESS you've got some means of isolating the two parts. On my system, I've got full-bore lever-type isolation valves on both the flow and return pipes of the CH side of the circuit. If I turn those off, I've still got a working primary circuit just running the HW.

[Hugh - Was Invisible]

Sounds good Roger. Never had such isolating valves. Perhaps I might add some next time I drain down. But then again the last time I had to drain down was because I had to replace the pump and it's isolating valves were useless.

[82045]

They rarely last longer than a pump if not operated from time to time.

[John Ledger]

OP here, Another bit of advice please. One of the rads I have fitted is like this one

Has anybody ever fitted one similar and how do I ensure I remove all the air? I can put two bleed vales at the top of the outer columns but how do I get the air out of the central ones. The rad is attached to the wall by 4 'spigots' so tipping it will be difficult, and I would imagine the majority of the air would just go to the top corner of each column. The rads are installed with solid piping not plastic. Any tips advice greatly appreciated.

Cheers

John

[Mark]

Also make sure you do not have a Primatic cylinder as draining the CH would also drain the DHW!

[Roger Mills]

I fitted my valves a couple of summers ago when I was in the process of removing each radiator in turn and washing it out - and then replacing the valves with a TRV one side and a drain-off lockshield the other side. I did this over a period of several weeks, and wanted to be able to use the boiler to heat the HW in the meantime.