Hi,
I was thinking of upgrading our CH system in the next month and like the idea of thermostatic rad valves. I already have two Honeywell VT117E on 2 bedroom radiators. I was going to buy another 6 and put them on some of the other rads in the house.
Is it a good idea to have a lot of TRV's in a system and I presume that the Honeywell ones are ok?
Thanks for any advice, Matthew
It's a good idea to stick TRVs on all rads, except the bypass rad (If there is one).
Honeywell will be OK
sponix
How do you know if you need a bypass rad ?
You *do* need a bypass for the case when all the other TRVs are closed and the boiler/pump need to dump the hot water until they realise it's time to turn off. It doesn't have to be a rad.
MBQ
Interesting. In my house at the moment all the rad's have TRV's, even the bathroom towel one which would seem to be the obvious candidate for the bypass rad. (Its a combi system btw)
When I say it doesn't have to be a rad, I believe some boilers incorporate the bypass. Ours is a pipe in the airing cupboard with a valve to restrict the flow like a lockshield.
MBQ
I thought the rad nearest the room stat should not have a TRV?
Or
Correct.
snip...
yes & ought to save you CH fuel bills if used sensibly. OTOH if you set all the TRVs to 27deg C you won't save on any bills, nor if you leave all your internal doors open.
You'll do best to make all valves TRV except for the bypass rad (if you have one - the bypass may be inside the boiler casing or in larger setups a separate pipe loop near the boiler). You also need to be cautious putting one in a room with a system controlling room thermostat, otherwise they may joust with each other. Had trouble here on one occasion with a rad which wouldn't turn on - the TRV was sitting in the air stream from a computer fan :-))
and I
sorry can't help with specific brands, but when I installed the CH here
5 years ago there were 2 types on the market - reversible and non-reversible. I checked on the manuactuer's help lines as to the type before buying. The reversible ones could be put on either the inlet or the outlet of the rad & are obviously more versatile. Non reversible had to go on the inlet end only. I used the reversible type & the only minor trouble has been a couple of times when the pin on which the thermostat operates, has jammed. It just needs a mild clout with a hammer to free it. It probably pays to vary the setting every so often to avoid the pin settling into a fixed position.Check for ease of removal of the thermostat head. No TRV turns off completely at normal house temperatures when the CH is off. (ie your house will normally be warmer than the 8deg C turn off of the TRV). So if you want to remove a rad for decorating you have to take off the head & screw on a cover to hold the pin completely down.
Most have a tab to set a tamper proof maximum ON. They vary as to how easy they are to set (& alter).
Also watch for orientation - normally best operation is when the head is horizontal away from the rad. Installing it vertically (upright) parallel to the edge of the rad is giving the TRV a sensing problem.
HTH
Even if you have some form of bypass, you still ought to have some form of interlock to turn off the boiler once the house is up to the required temperature. This is usually done with a room thermostat, and if you have a room stat then the rad in that room should not be fitted with a TRV.
If don't have a room stat then you need some other form of interlock. You could use a flow switch to detect when flow is effectively shut off through all the TRVs (or when flow occurs through a spring loaded bypass loop) to also shut off the boiler. This will not only save fuel, but also prolong the life of the pump and boiler.
In message , jim_in snipped-for-privacy@hotmail.com writes
Well, you just shouldn't do it really.
I imagine Honeywell are fine. I've always used Drayton, but any good brand should be ok, I don't think cheapos are worth it.
Er if your house is warmer than your TRV setting then surely the TRV would be closed down?
but it's not wise to rely on this as it may open at an inopportune moment, so yes it's best to use the cap if you ahve it.
Theoretically , but they all seemed to work fine in my old house when vertically mounted.
The instructions with my TRVs(made by Yorkshire) also recommend fitting to the return(coldest) side of the radiators.
Keith G. Powell
The control system starts to get a bit complicated with flow switches. Once the flow switch has detected low flow and switched everything off, there will be *no* flow - so what turns it on again when the TRVs open? With the alternative, of sensing by-pass flow, the system will hunt. Surely, a room stat is by far the simplest way of achieving boiler interlock?!
You would nee some other mechanism. Could be a timer, or a pipe stat etc...
Yup agreed! and these days of wireless stats dead easy to install even if not provided to start with.
Any gotchas with wireless stats? What happends when the batteries die? Good/bad makes etc.
Thanks Pete
On loss of comms or battery failure you can default the Honeywell CM6* series to either totally off or 20% on / 80% off.
Is the stat and receiver a matched pair or will I be able to select a channel and turn my neighbour's CH on and off? :-)
Matched
snip
sorry got a trifle muddled there. Problem (which I've experienced) is that the minimum setting on a TRV is about 8deg. So if the room air temperature is less than 8deg then the TRV opens regardless of whether the CH is On or Off. This is when you need the cap if you wish to take off the radiator for decorating. Also in practice TRVs do not make a sharp cut off of flow at a specific operating point.
Hope that explains the point.
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