TRV valves - replace lockshield at same time?


I am getting TRVs put on my 25 rad central heating system.... The plumber is putting in Drayton TRV-4's on most of the rads, aswell as power-flushing whilst it is drained.
Wondered whether it is worthwhile spending the extra 300 he has quoted to replace the remaining existing valve on each rad with a new lockshield.
Is it worthwhile replacing the other valve on each rad when you install TRVs?? I personally dont think it is as you open the lockshield fully anyway and dont use it at all. The only downside might be is if you ever come to remove a radiator and the lockshield is leaking - you'd have to drain the system down again?
Wasnt going to bother but wished to check others thoughts.
Thanks, Nick.
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Nick Dawson wrote:

mentioned. If they work then leave them. 300 seems an awful lot just to replace valves but I suppose there might be a stuck olive or two. Wickes do a pack of five 15mm valves for 9.29 or so. So you could do my standard semi for less than 15 in parts plus labour.
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Malc
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spindle I'd be inclined to keep them.
BTW, TRV systems need to be balanced too so the lockshield shouldn't be full open.
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fred
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"fred" wrote

While you are having what appears to be a fairly major ch overhaul, I would do it! And if you are fitting decent TRVs like Draytons, go for a decent l/s like Pegler Terriers. You don't say how old the system is, but if it is any age at all and needs power flushing, there is obviously a degree of crud in the system. This can deposit in the valve bodies (as these are a point of max restriction in the heating ciruit) and can lead to poor valve performance and in the worst case blockage. Power flushing is not a cure all and the efficiency of this method of cleaning can be reduced by intricate pipe routing which slows the water velocity. It would be interesting to ask for a (small) radiator to be removed after the power flushing (before new valves are fitted), particularly an end-of-line rad, and tipped up/manually flushed into a bowl. Make sure you are there to see the results yourself. This would give a fair indication of the effectiveness of the clean. Easy job and not much to ask if you are paying 100s for the flushing.
These recommendations are not hearsay or guess work, as I have recently overhauled a heating system in a 1970s property which had been suffering pump over issues and was therefore pretty cruddy.
If you intend to stay in the property, consider fitting MagnaClean or Boiler Buddy filters to keep crud at bay. Also consider the controllability of the current system and whether it could be easily improved.
HTH
Phil
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That's an interesting comment in your final sentence and I find it a little baffling. Can you enlighten me? !
I fitted TRV's to all my radiators last autumn (bar the hall radiator where the roomstat is located). AIUI, radiators without TRVs are balanced so that each radiator supplies sufficient heat for the room in question. A TRV equipped rad will, of course, heat the room up to the required temp as set on the valve, and then shut down. I'm baffled as to why balancing should be necessary on such a set-up. I've been using my new system, with the lock-shield valves fully open, throughout the winter and have found a dramatic improvement over past winters. Temperatures in each room have remained far more stable and constant without any need to be constantly adjusting the room stat.
I'm genuinely intrigued by your comment and would appreciate your comments.
Uno-Hoo!
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temperature and they start to close down. Until then your system behaves just like they aren't there and you need to balance the outputs of the radiators to ensure than the house heats up evenly. If you don't do that then you risk having the room closest the boiler with the largest radiator stealing all the heat until that room reaches temperature (and the TRV closes down) then the next nearest with the next largest radiator and so on until the most distant room with the smallest radiator finally gets some heat. The house will eventually get warm throughout but it is not the most efficient or quickest way of going about it. In the worst case, a large rad that is close to the boiler and wide open will raise the temperature of the return flow higher than it should making a modulating boiler turn itself down or a less sophisticated boiler start cycling. This will result in longer warm up time or poor control.
Think of TRVs as devices to stop rooms becoming overheated, not as balancing mechanisms.
It may be that your system has a pretty neutral balance to start with so the extremes above do not apply or it may be that your previous balance settings were throttling the system flow and slowing warm up. The latter was certainly the case on my system on my first attempt at balancing and opening it up a little and following the balancing procedure on the uk.d-i-y faq site improved matters.
To balance a TRV system, open the TRVs fully and follow the procedure on the uk.d-i-y faq then set your desired control temperature on the TRVs
HTH
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Thanks for that Fred - most informative! I'll do as you suggest.
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