In article ,
Simon C wrote:
Do I just drain down the whole system and then start fitting the
vavles?

Yup.

FWIW, it's worth buying good quality TRVs from a plumber's merchant rather
than shed own brands. Drayton is a decent make. TRVs don't last for ever,
but good ones might have 3-4 times the life of others but don't cost that
much more.

Do I need to remove the radiator to fit the valve?

No. But you might have to replace the short pipe going into the rad,
depending on the design of the TRV - but it comes with the TRV, so is
simple to see if it's different.
You need the correct tool for this - an allen key that fits inside the
pipe. Not expensive.

Each rad has a control knob to turn off the water to the rad - do I
replace these with the vavles, or do they go on the other side of the
rad?

You need to check the instructions with the TRV. Some must go on the input
- some don't matter.

FWIW, the two original valves are identical - just the knobs are
different. The idea being one is preset to balance the system and is
fitted with a cap to prevent tampering, the other to turn off the rad or
adjust by the householder if needed.

To determine which is the input, feel the pipes when the system is first
switched on. The feed will get hot before the return. Hopefully this will
be the side with the user adjustable valve, but I'd still check. A TRV
fitted to the 'wrong' side will likely be noisy and may not work properly.
If the system was working well before, try not to alter the preset valve,
or if you do, count the number of turns so you can put it back to where it
was afterwards. The procedure for the adjustment of these from scratch (if
needed) is covered in the FAQ under balancing the system.

Should I refill the system with an inhibitor and cleaning solution?
Do I need to fit the valves to radiators in any order and do I need to
carry out any procedure to refil other than make sure all vavles are
fitted then turn on the water?

The rads, of course, will need bleeding of air.

I'd fill with plain water, use for a couple of days to check for leaks,
then drain down enough to add the inhibitor.

You might well get an airlock. If it's only say one rad effected, turn the
others off and run the pump at max - this might clear the airlock.

The other way is to connect a mains water hose to the drain point and
force water back into the system that way. That should cure the airlock.

--
*If at first you do succeed, try not to look too astonished.

Dave Plowman London SW
To e-mail, change noise into sound.