Fitting TRV to radiators

[vw-stuff]

Hello all

I am looking forward to autumn/winter and want to fit TRV's to the upstairs rads....upstairs always get hot whilst the living room downstairs if several degrees cooler. I know I have to drain the CH system to fit TRV's but will the TRV be a direct replacement for the existing valves? The fittings on the TRV look slightly different in size to the threads on the rads. Do I have to replace anything?

I have bough some B&Q TRV's, only cheap ones but I am not thinking about getting a decent brand. I hear that cheap ones can suffer from water hammer and can often stick.

Any comments or advice would be greatly appreciated.

Thanks

[Derryck Croker]

Only enough to drain the upstairs rads if you're only doing those. I've heard that you can seal the feed and vent pipes to airlock the system to stop water escaping as an alternative.

Should all fit together nicely, you'll need a radiator allen key to unscrew the fittings from the radiators and some ptfe tape to seal the threads when you put the new ones in.

You may or may not need to adjust the length of the actual pipes.

I have bough some B&Q TRV's, only cheap ones but I am not thinking about

Check that you put the valves on the correct side of the rads.

[vw-stuff]

Where is the feed and vent pipes? Will they be in the loft with the CH water tank?

Do I have to remove the threads from the rad? Does the TRV thread screw directly into the rad then replacing the old thread?

I have bought reversible TRV's, they have arrows pointing in both directions on the 90 degree bend. These can go on either end can't they?

[Derryck Croker]

Feed pipe from the CH cold water tank, vent from the hot out of the cylinder. I couldn't make this work when I tried it though, so would recommend partial draining.

Undo the nuts on the valve and pull the valve off - it should look the same as the thermo one. I don't think you have to dismantle the rad any further so you probably don't need the allen key. But don't do the job on a Sunday afternoon just as the shops close...

Sounds like it, but you may as well put it on the correct end anyway unless there's a good reason not to.

[vw-stuff]

Which is the correct end?

[gilbert]

The FLOW. But check the instructions with your TRV. Most seem to be 'either-ended' nowadays - earlier makes were nearly all fitted to the flow (the end that gets hot first!:O) Cheers Gilbert

[vw-stuff]

Have read that fitting the trv to the return can help reduce water hammer?? Anyone confirm/deny this.

[gilbert]

I would imagine it was (or certainly used to be) more likely. Usually, a TRV has a spindle which is pushed by the actuator. If the spindle pushes against the flow it will steadily exert pressure until it closes. If the water flow is from 'behind' the spindle (i.e. out of the radiator) it can suddenly bang the valve shut against the seat as a result of the combined flow of water and direction of the valve seat. Bit like reseating a bath plug while the water is emptying. Cheers Gilbert