Thinking about retro-fitting TRVs to some rads, but we don't know as yet which way they "flow" - I believe you can get around that by fitting a TRV that works on either the "input" or "output" side, but Screwfix use different wording, such as...
Bi-Directional Valve Body Reversible Flow
Are these the same, or is there a fundamental difference between the two, like the "T" piece would need adjusting to suit or something ?!?
Ta :-}
Some TRVs don't *mind* which way the flow is - so you can fit them to either end without knowing the flow direction in advance. Others can be *set* to work one way or the other by rotating a bit inside which you can't get at once it's fitted - so for these you *do* need to know the flow direction before fitting them. 'Bi-directional' and 'Reversible' respectively would probably apply to the two types which I have described.
Having said that, it's hardly rocket science to find out which is the input and output on each rad. If you can't easily trace the pipework, you just have to run the system for a few minutes to see which pipe gets hot first. Before replacing all my valves, I marked the 'hot' side of each rad with a little red blob from a felt-tip pen, near the valve connection.
If you're taking the rads off to replace ordinary handwheel valves with TRVs, why not replace the lockshields with drain-off valves at the same time. It makes it a lot easier next time you need to drain the rad - for decorating, etc.
If you look at a Drayton (Invensys) TRV, you will see a bi-directional arrow. You can fit them either way around without adjusting anything.
I've heard Pelgar is also a good make (no personal experience), but otherwise most of the TRVs you'll find, particularly cheap ones, are junk in comparison, and probably best avoided unless you're just after something that looks the part for regulatory reasons.
In message , Colin Wilson writes
Turn on and see which end gets hot first ?
Colin Wilson submitted this idea :
Turn the valves off, heating on, then open the valve on the rads one at a time. The end of the rad which heats up first is the input pipe. Simples.
Yebbut... the rad in question is drained and disconnected :-}
It's also leaking from one of the valves which came a little "unseated" when attempting to reconnect it, but we won't go there...
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