Fitting Radiator Thermostatic Valves

[Simon C]

Hi there..

I know there are a few posts in this group realting to this topic, but I wanted an idea of doing the whole job...

I've got a pretty old gravity hotwater setup with 15mm pipes to the rads. I have already bought a few thermostatic vavles and need some advice on fitting.. I've found a drain point near my boiler - and I know I'll need to protect the carpet when I loosen the pipes to the rads...but here's a few things I'm not sure on..

Do I just drain down the whole system and then start fitting the vavles? Do I need to remove the radiator to fit the valve? 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? 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?

Thanks alot!

Simon

[Simon C]

Hi there..

I know there are a few posts in this group realting to this topic, but I wanted an idea of doing the whole job...

I've got a pretty old gravity hotwater setup with 15mm pipes to the rads. I have already bought a few thermostatic vavles and need some advice on fitting.. I've found a drain point near my boiler - and I know I'll need to protect the carpet when I loosen the pipes to the rads...but here's a few things I'm not sure on..

Do I just drain down the whole system and then start fitting the vavles? Do I need to remove the radiator to fit the valve? 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? 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?

Thanks alot!

Simon

[Dave Plowman (News)]

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.

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.

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.

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.

[Andrew Gabriel]

I found a 1/2" cold chisel with a hexagonal shaft to get the spanner on was just perfect.

[Dave Plowman (News)]

I tend to use one from my socket set.

The correct tool gives you the thingy for fitting the bleed screws too, though. And they're a bit more difficult to find a bodge for. ;-)

[Paul R]

Personally, I haven't drained down the system on two TRV replacements (different properties). You can buy a 'kit' from the plumbers merchant which is basically two rubber bungs, to seal up the system at the expansion tank to create a vacuum. This allows you to open the system up at ONE point, e.g. remove a single valve from a radiator, with the other radiator control valve turned OFF (recommend draining down the radiator first though). The vacuum created holds the water in the system and allows you to work on replacing the valve.

This has worked very well, many times for me.

Paul R

[Dave Liquorice]

Otherwise know as a "tail".

I don't think I've ever found a tail that matches a new valve, TRV or ordinary. Thats on the various vintage rads here and in my Bristol flat, they where only about 10 years old when I swapped 'em.

When changing tails you'll need some PTFE tape to wrap around the threads to seal them. Half a dozen or so turns in the direction that means it stays on the thread and is not pushed off by the turning.

But the correct modern doesn't fit imperial tails. Found that out last week. B-( Had to grind a good 1/2mm off each face of one end to get it to fit. Oh and tail thread sizes haven't changed. B-)

[Dave Plowman (News)]

Good grief. I'm on my third set of TRVs in this house, but all are the same. Changed to the current set only last year. Have they changed since then, or before I installed the first lot?

[Dave Liquorice]

I'm refering to the hex hole in a *very* old tail. At a minimum I'd say 20 years old a more realistic date might be 30 years. This part of the house is plumbed in imperial pipe, when did metric pipe come in?