What are the consequences of unidirectional TRVs fitted to outlet not inlet?

[dch0jmh]

I have just had a new combi boiler (Worcester 36 CDi Compact) fitted as a replacement for my trusty Worcester 350 Combi. The system was powerflushed as well (with a Magnacleanse filter on the machine, though it didn't take as long as I'd have expected: about 3 hours for a 13-rad system). A Magnaclean was fitted too. Most of the radiators now work well, but 3 don't, so I've been teaching myself about balancing. I don't think the problem is balance, though, because two of the rads seem to get no flow at all even when they are fully open (at both ends) and every other rad on the system (except the one intended to allow the boiler some flow) is fully closed. I can hear the water starting to flow in all but those 3 as I unscrew the lockshield valve.

Most of that's by the by, though I'd welcome any comments on how good a case I have in going back to the installer to tell them that the powerflush wasn't thorough enough.

But my question is this: in balancing the system as best I can, I have found that 4 of the 10 rads with TRVs have them fitted to the return side, not the flow side. They are quite old Danfoss TRVs (with a big white cap and a black wheel underneath, which unlocks with a tab that you prize out with a small screwdriver). They _do_ have an arrow on the copper casing that points into the rad, and I presume this means they are unidirectional not bidirectional. [Am I right on that?]. But actually they have been in place for between 10 and 18 years (I think they went in in two batches), and I haven't actually observed any problems with them. They certainly seem to stop the audible flow in the rad progressively as I turn them down.

So what exactly are the problems I might have through these TRVs being mounted on the outlet? Are they serious enough to justify getting someone in to swap the TRVs and lockshield valves around?

[I'm not sure whether to ask the boiler installer to do it: they're a big firm with a decent reputation, and they may have to drain the system anyway if the powerflush needs redoing; but asking them to fix a pre-existing problem on the system might give them too much of an "out" with respect to the powerflush issue.]

Any input is welcome, and thank you for reading my rather long explanation!

 

[Ch4 plumbing]

My advice would be to ring the installer and explain the problem and the guy will pop back and sort for you.

 

[Neil K]

Your installer should have balanced the system and (not having a dig at you, I know what you mean, just a bit of what we call back home edumacation) instead of inlet and outlet they're called flow and return. From reading what you've read quickly, the old trvs sound like one directional trvs.

 

[missplumb]

generally ive found that having the directional trvs on in the wrong direction makes the system quite noisy, a sort of vibrating noise as the jumper in the valve chatters against its seat. i was always told that trv's should be fitted to the return (outlet) side of the radiator and fitted with the valve horizontally as then heat from the radiator will have a lesser effect on the wax capsule inside the valve sensor and more from the cooler air temperature around the valve.
as for balancing, this shouldnt make that much of a difference, get them back and just say some of the rads arent working, a big decent company will sort it out no probs.

 

[Chalked]

Do the radiators that don't work have a trv? If they do, the valve is probably stuck in the off position. It's a very simple cure, which your installer will know how to remedy.

Don't be frightened to call them back to get the heating working properly.

 

[Unregistered]

Do the radiators that don't work have a trv? If they do, the valve is probably stuck in the off position. It's a very simple cure, which your installer will know how to remedy.

Don't be frightened to call them back to get the heating working properly.

Actually no. The two that get no flow are a plinth radiator with just two screwdriver-turned shutoff valves and a small towel-rail with no towel-rail with an old-fashioned knob and a lockshield (both fully open). I was hoping to use the latter as the bypass rad to allow some flow in the system when everything else is switched off.

I've learned in the last few days how to take the head off my TRVs and check that the pin is moving freely, so far all that I've checked are fine.

 

[Unregistered]

That should have said "a small towel rail with just an old-fashioned knob and a lockshield".