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Knock on effective of balancing radiators

 
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Thermostats, Volumisers, Buffer Tanks, TRVs, Pumps, Piping, Valves, Radiators & Controls
Last Post by JamesPa 2 months ago
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JamesPa
 JamesPa
(@jamespa)
Illustrious Member Moderator
Joined: 3 years ago
Posts: 4800
24/02/2026 9:01 am  

Posted by: @bash
↑

What is the rough amount of flow that I'll get from the first quarter turn, would it be around half?

It's very dependent on the lsv, heat geek did a series of experiments (search for 'valve authority') and found the control range varied from 0.25 turns to 2 turns depending on model.

 


This post was modified 2 months ago 2 times by JamesPa

4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.


   
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Mars
 Mars
(@editor)
Illustrious Member Admin
Joined: 5 years ago
Posts: 4550
24/02/2026 9:19 am  

Posted by: @bash
↑

I was starting to come to the conclusion that that FRVs whilst useful, could end up being the best part of £1000 to fit and I don't really want to pay that

We’ve covered some of this over DM, but for everyone else following along, there’s potentially a “smart” alternative to FRVs due to hit the market later this year. Different manufacturer, different approach. I’ve signed an NDA so can’t share specifics, but the key point is that it dynamically balances the system in response to real heating demand rather than relying on static pre-set flow limits. 

On conventional FRVs, our experience has been mixed. In principle, they’re a tidy solution. Do the room-by-room heat loss, calculate the required litres per minute, set the valve accordingly and they should hold that flow rate regardless of pressure fluctuations elsewhere in the system. In practice, they did a reasonable job for us at “normal” flows.

Where it became problematic was at very low flow rates. When we tried throttling certain radiators down to around or under 0.5 L/min, the valve didn’t appear to modulate… instead it effectively shut the radiator off. We saw this repeatedly at settings below roughly 1 L/min across five rads. The radiator would go stone cold, forcing us to increase the setting to over 1 L/min, which was more than that emitter actually required from a design perspective.

So while FRVs can be useful, particularly in systems with pressure variability, I don’t think they’re a silver bullet.


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bobflux
 bobflux
(@bobflux)
Estimable Member Member
Joined: 2 months ago
Posts: 84
24/02/2026 10:05 am  

I find it quite ironic that most of this heating/plumbing business is about controlling flow and pressure, without actually measuring flow and pressure! Strange rules for a game, when you think about it...

Now a ultrasonic heat meter costs 20€ in medium quantity on alibaba... Motorized ball valve costs 10€... Pressure sensors are also quite cheap... The call of over engineering is too hard to resist 🤣 

 

 

 



   
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JamesPa
 JamesPa
(@jamespa)
Illustrious Member Moderator
Joined: 3 years ago
Posts: 4800
24/02/2026 10:18 am  

Posted by: @bobflux
↑

I find it quite ironic that most of this heating/plumbing business is about controlling flow and pressure, without actually measuring flow and pressure! Strange rules for a game, when you think about it...

Thats a very astute observation.  Its like an electrician working without any test equipment!


4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.


   
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Morgan
 Morgan
(@morgan)
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Joined: 5 years ago
Posts: 698
24/02/2026 10:41 am  

I'm looking for a cap to replace the TRV. Whilst all of mine downstairs are fully open, I'm given to understand that there is still pressure on the valve that constricts the flow. I want to remove the TRV but not leave the valve exposed. All I see are decorator caps that achieve the opposite by completely closing the valve. Ideas please.


This post was modified 2 months ago 2 times by Morgan

Retrofitted 11.2kw Mitsubishi Ecodan to new radiators commissioned November 2021.
14 x 500w Monocrystalline solar panels.

2 ESS Smile G3 10.1 batteries.
ESS Smile G3 5kw inverter.


   
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 Bash
(@bash)
Reputable Member Member
Joined: 7 months ago
Posts: 188
Topic starter 24/02/2026 10:58 am  

@jamespa 

I found the valve authority video which is very helpful.

We have Pegler Terrier valves, but I cannot find any info on what the valve authority is like on these.



   
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JamesPa
 JamesPa
(@jamespa)
Illustrious Member Moderator
Joined: 3 years ago
Posts: 4800
24/02/2026 11:00 am  

Posted by: @morgan
↑

I'm looking for a cap to replace the TRV. Whilst all of mine downstairs are fully open, I'm given to understand that there is still pressure on the valve that constricts the flow. I want to remove the TRV but not leave the valve exposed. All I see are decorator caps that achieve the opposite by completely closing the valve. Ideas please.

Decorators caps, not screwed down (they can actually be used to adjust the flow) or the original head just balanced on top.  I do the second of these but if you have children or dogs they will get knocked off so perhaps in this case the first is better.


4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.


   
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