Thermostatic valve failure modes?

[Mike Tomlinson]

Have a couple of rads with thermostatic valves that don't seem to work - there's very little margin in turning the knob between getting full-on and full-off. I think the valve heads are the liquid-filled type.

What's the typical failure mode of those?

Replaced one which had a cracked plastic collar. Local DIY place didnt sell valve heads separately but sold me a complete valve and I transferred the head from that to the rad ok. Are they all interchangeable?

(I know, a funny time to be asking heating-related questions, just preparing for winter)

[Dave Liquorice]

Sticky mechanisium. Though more often than not they stick closed after being foreced hard shut during the summer. Gentle tap with a small hammer sometimes frees them off or you might need to get some pliers onto the pin and work it up and down a few times.

Probably the thread holding the head into the radiator tail is almsot certainly going to be standard (3/4" BSP?). What might vary is the distance from valve seat to head seat. A small variation probably won't present any problems but if the tail has bigger gap than the reach of head...

[DerbyBorn]

"Dave Liquorice" wrote in news: [e-mail]:

I think they work as you described - a few degrees of turn of the valve makes a significant difference to the flow. I can hear the cut-off point if I put my ear to the radiator. Can be useful.

[Mike Tomlinson]

En el artículo , Dave Liquorice escribió:

The mech is ok (freed off and lubed with a squirt of WD40), the pin moves up and down freely. Push the pin down, the rad begins to cool. Let it rise, and the rad gets hot again. It's just the valve head that isn't working.

Sorry, I meant the are valve *heads* interchangeable, not the valve itself. It would be nice if I could swap the heads without having to drain and change the valve too.

[A.Lee]

Some are, it's a case of try them and see. Some do, some are nowhere near.