TRV upgrade on air source system. Drayton TRV4?

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Hi, I am replacing a couple of radiators with (bigger) Stelrad K2s, to compensate for lower temp Air Source heat pumps (55deg). The originals were fitted with Drayton/Invensys RT212 valves in 2004.

Remaining rads will be replaced next Summer, but these need to be done now.

The air source installer recommended I try to maximise flow, and pipework is gradually being upgraded from 22/15mm to 28/22/15mm wherever possible.

The Lifestyle valves have not been unreliable, but may not have been as responsive as they might be, although the previous boiler was oil fired with gravity DHW and a pretty old thermostat.

TRV4s are highly recommended here and I am looking to fit these to the majority of rads. A couple of comments though, have planted some doubt on whether this is worthwhile?

The latest TRV4 has apparently a more restricted flow rate, and other suggestions that they may use the same valve body as the existing TRVs. If there is no difference in the main valve, maybe I should only change the heads? though this would not save much if any money, and the existing valves are far from new.

My main attraction to TRV4s is they are liquid filled and said to be more sensitive to ambient room temp - this is particularly important in the living room where a wood burner may often mean the heating would be more beneficial circulating around the rest of the house.

Looking at the valve body of a removed RT212, even this has a max 7-8mm aperture. I have been hesitant whether to use TRVs at all, as this is supposed to be a 'whole house' solution, keeping the house generally around 18-19 degrees and boosting when required. The Installers, Ecovision, say 50% TRV's will be fine, maintaining flow, while diverting the energy to where its most needed.

Is there a reliable, responsive thermostatic valve which provides full flow when open? Also any recommendations on flow or return for valve location would be welcome, I know its either/or but it would be good to get the best possible result.

Thanks.
 
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Looking at the valve body of a removed RT212, even this has a max 7-8mm aperture. ... Is there a reliable, responsive thermostatic valve which provides full flow when open?
The opening in a TRV is small compared to the area of a 15mm pipe, but a TRV only needs to carry the flow required by the radiator it is attached to, not the full flow which a 15mm pipe is capable of carrying.

A TRV4 can handle up to 6kW.

The body of the RT212 is identical to that of the TRV4, it's just the head which is different.

As far as I know the TRV4 has not been updated, apart from the availability of an all-white version.

A full flow TRV is the last thing you need. After all the lockshield valve on the other end will be restricting the flow through the radiator.
 
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You are wasting your time changing TRV and pipework.
Completely unnecessary.

All that matters is the flow through the air source heat pump is sufficient for the pump itself. I somehow doubt the TRV will be working anyway as the radiators will be flat out all the time trying to keep the rooms warm with a lower radiator temperature.

I would suggest a heat store tank if you have the room to allow the pump to run full pelt until the tank hit temperature.

I hope you haven't made the mistake of doing away with the oil boiler as this should have been kept as a booster for very cold weather.
 
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Thanks folks for the replies, really useful info. Very valid point on the TRV flow rate.

I have a 300l heat store, only problem is its further from the bathrooms than the original airing cupboard, and takes ages for HW to flow from the tap (Kitchen's great though). Maybe I should use some new copper to run a HW circulation loop instead?

Still have the old boiler, though not in circuit. I'm hoping to use a good sized woodburner (8Kw+) as a booster.

So prob not worth forking out on a bunch of TRV4's then. Will need to buy some new lockshields though, any recommendations?
 
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Thanks folks for the replies, really useful info. Very valid point on the TRV flow rate.

I have a 300l heat store, only problem is its further from the bathrooms than the original airing cupboard, and takes ages for HW to flow from the tap (Kitchen's great though). Maybe I should use some new copper to run a HW circulation loop instead?

Still have the old boiler, though not in circuit. I'm hoping to use a good sized woodburner (8Kw+) as a booster.

So prob not worth forking out on a bunch of TRV4's then. Will need to buy some new lockshields though, any recommendations?

If you already have a heat store the air source heat pump is heating this so has all the flow it needs to work at it's best. Can't understand why the installed would suggest you need to do anything with your pipework. I assume the heat store is used to then run the central heating. Just normal radiator packs lockshield and trv are fine nothing special.
Woodburner waste of time but that's just my opinion (people will see sense eventually) Use the old boiler as a second heat source for the heat store to bring the temperature of the water up when it's very cold. Installer should have done this. Heat pump isn't going to do it when it's really cold.
 
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