Lockshield valves wide open - why?


Postby midknight » Sun Nov 30, 2008 8:43 am

New house new Ariston A30 MFFI combi-boiler fitted.

4 rads downstairs - cloak hall lounge x 2

5 rads 1st floor - 2 beds bath ensuite hall

1 rad 2nd floor - bed

Anyone know why the engineer would leave a system with them all wide open. Is this best practice now?

Thanks - from muddled
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Postby htg engineer » Sun Nov 30, 2008 12:24 pm

Quite common with new installations, he's probably just an installer - wants to be in and out.

If all the radiators get hot, and the rooms heat up - then the system works. But to get the best from the system you want about 12 degree temperature difference between the flow and return to each rad, this means heat is being emitted to the room and it's not just circulating round the system.

On a new system all lockshields valves fully open - probably no problem, but as the system parts get older (pump etc) you may find some rads will get hotter than others - then balancing will be necessary.

In a new house I would drain, flush and add inhibitor - as it probably hasn't been added - there's not many building cmpanies that bother or specify this to the contract engineers.


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Postby chris_on_tour2002 » Mon Dec 01, 2008 8:37 am

has he fitted thermostatic rad valves to the radiators? if so the lockshields are meant to be fully open and at least one rad must have non-TRV valves fittedm also with valves fullt open.

as htg says, on a new system no problem, unless you want to be fussy about the 12 degree temp difference across the flow & return. maybe later on you will need to make adjustments.
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Postby AdamsHeating » Mon Dec 01, 2008 2:44 pm

wo wo wo wo wo back your cart up a bit there son... I've been installing TVR's and balancing my installs to get a differential of 11 degrees for a while now, are you telling me I could just walk away instead of balancing?!
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Postby htg engineer » Mon Dec 01, 2008 6:20 pm

AdamsHeating - unless you installed midknight's heating system, I can't see where you got the personal connection from ????

Fitting TVR's to heating systems ? or Trv's :-)


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Postby AdamsHeating » Mon Dec 01, 2008 6:41 pm

Good eyes htg! I should have learnt to spell by now surely?

yeah, TVR's to heating systems... doh! It would get pretty expensive if I started fitting 7 cerberas in ever house, not to mention the space it would take up.

My point was that chris states that the lockshields should be fully open if you install TRV's but I always balance the system to get an 11degree differential, should I do it or not? I think that ties in with the original question... maybe!!!?!!!
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Postby chris_on_tour2002 » Tue Dec 02, 2008 12:57 am

leaving aside the ethical argument for a moment (before a hairy lentil eater in sunday market knitwear picks me up on it :D) - if we all balanced our heating systems for optimum performance then perhaps the glaciers wouldn't be retreating at the rate that they currently are, but let's keep it technical for the purposes of this discussion.

adamsheating - if you always balance your new installs when TRVs are used then good for you! cannot be faulted and you are surely in the minority.

with permission i would like to retract my use of the word "should" from my post. though in my defence there are TRVs available now that categorically state that the lockshield valves remain fully open (i admit that i was not assuming that these were the type fitted in this case). i found this extract from GN3 which the administrator will hopefully permit as it's only a tiny extract from the overall article:

"One of the main causes of poor TRV control is the UK use of a minimum pipe size of 15mm/½". In general, UK ½" TRVs passing approximately 3600W when fully open (at system start up) in a 11°C delta T situation with a typical pressure differential of 10kPa. Since the average radiator size is 1200W, there are some 2400W to be taken out. This “Overflow” should, in theory be regulated out by means of the radiator lockshield valve, but this is almost never done.

The selecting of TRV bodies having variable Kv values is the ideal solution. This easy to regulate method of optimising the individual radiator flow requirement gives the site engineer the opportunity to preset each valve relative to a heat output from the radiator schedule. The lockshield valve remains fully open."

additionally there is a recommendation to fit DPCVs to all systems fitted with TRVs to prolong the life of valves and other system components.

the purpose of the reply was to try to put midknight's mind at ease a little (though this thread may have had the opposite effect by now!) and frankly HTG had already covered it quite nicely in his reply: "Quite common with new installations, he's probably just an installer - wants to be in and out. If all the radiators get hot, and the rooms heat up - then the system works. But to get the best from the system you want about 12 degree temperature difference between the flow and return to each rad..."

in hindsight i should have left well alone!

to answer midnknight's final question, no it is not best practice to leave the lockshields fully open though it is, rightly or wrongly, common practice.

balancing your system will offer improved longevity, efficiency and running costs - though by how much is impossible to say. you'd also be helping the good people of norfolk to get a decent night's sleep in, happy in the knowledge that you have kept the north sea from lapping over the front doorstep for another night. and on that thought, i'm off to buy a fleet of TVRs :D
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Postby AdamsHeating » Tue Dec 02, 2008 3:51 pm

Looks like that one has been well and truly put to bed! Cheers Chris!
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Postby C23kW » Sat Dec 13, 2008 1:47 pm

listen girls and boys....
simply - leave all your locksheild valves open and control the flow with the TRV's by balancing.
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Postby htg engineer » Sat Dec 13, 2008 6:27 pm

Rubbish...... the lockshield is for balancing the system.

The TRV is for comfort control - controlling the temp of each room.


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Postby Steve the gas » Sun Dec 14, 2008 4:01 am

Well said Htg,
If all LSV's are open and all performing good, then, it could be the system is perfectly sized!!
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Postby midknight » Sun Dec 14, 2008 5:46 pm

Thanks for every reply - much appreciated.

Drayton TRV`s were fitted on all except the hall radiator. Most are run in 15mm and the rest in 10mm pipe.
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