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Help me keep the faith with my air source heat pump installation

 
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Air Source Heat Pumps (ASHPs)
Last Post by AdamK 1 week ago
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JamesPa
 JamesPa
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05/11/2025 9:28 am  

Posted by: @adamk
↑

@jamespa hopefully after the rad balancing it will perform better, as I think at the moment the water is short circuiting back to the hp through the fully open lockshields, though I’ve done some very basic balancing recently to see if it helps. Essentially I don’t think the hp is seeing the whole system due to the unbalanced rads.

Let's hope so.  It will be interesting to observe whether they balance for deltat or for room temperature.  I'm guessing the former as it's easier.  It's also a good starting point from which to tweak to get room temps right, if the loss calculations were sufficiently out to affect them materially.

 


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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DREI
 DREI
(@drei)
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05/11/2025 9:52 am  

Sorry to ask a silly question, but how to you actually balance your radiators?



   
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Majordennisbloodnok
 Majordennisbloodnok
(@majordennisbloodnok)
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05/11/2025 9:55 am  

Posted by: @drei
↑

Sorry to ask a silly question, but how to you actually balance your radiators?

Not a silly question in the slightest, @drei.

We even have an article for it. Heat Pump Radiator Tuning | Renewable Heating Hub

 


105 m2 bungalow in South East England
Mitsubishi Ecodan 8.5 kW air source heat pump
18 x 360W solar panels
1 x 6 kW GroWatt battery and SPH5000 inverter
1 x Myenergi Zappi
1 x VW ID3
Raised beds for home-grown veg and chickens for eggs

"Semper in excretia; sumus solum profundum variat"


   
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JamesPa
 JamesPa
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05/11/2025 10:01 am  

Posted by: @drei
↑

Sorry to ask a silly question, but how to you actually balance your radiators?

There is no such thing as a silly question!

@toodles wrote an article on balancing radiators:

https://renewableheatinghub.co.uk/radiator-balancing-lockshield-valve-guide/

You can balance for equal deltat or for room temp.  The two are the same if the design is perfect, which of course it isn't.  A good way is probably first to balance for deltat and then tweak from there.

I found it fairly easy over a period of a few days.  Rooms share heat so it doesn't have to be that accurate to give a comfortable result.


This post was modified 4 months ago 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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 AdamK
(@adamk)
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Topic starter 06/11/2025 11:17 pm  

They’ve had to cancel the radiator balancing at the last minute for similar problems as they’ve used before, sickness or vehicle problems, bit of a habit with them.

anyway was checking an old rad lockshield in preparation of the visit and found the rad sounded hollow.

ended up bleeding enough air out of it that the pressure went from 1.5bar to 0. So that would have caused some problems with volume.

also discovered they broke a bread screw off on another dual panel rad downstairs. Hopefully it has self bled as it’s quite short at about 430mm approx.



   
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 AgentGeorge
(@agentgeorge)
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Posts: 149
07/11/2025 7:57 am  

@adamk downstairs rads are less prone to airlocks, you can replace the broken bleed screw, you can get a set of two from a plumbers to replace both the blind side and the adjuster side.

Shut off both valves, unscrew the broken valve, slowly, expect some water to escape. Replace valve and use ptfe on it.

alternatively get the numpty that broke it to fix it



   
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 AdamK
(@adamk)
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Topic starter 09/11/2025 9:29 am  

@agentgeorge this is on a 30 year old rad at a guess. They’re like an odd little insert that is about 10-15mm in size with the bleed screw in the centre.

on another question, what’s a decent bleed key? I’ve got 2 and on some rads they won’t crack the bleed screw off.



   
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JamesPa
 JamesPa
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Posts: 4292
09/11/2025 9:47 am  

Posted by: @adamk
↑

what’s a decent bleed key? 

made of brass not plastic, proper square hole same shape as bleed screw.

I did a quick search and they seem relatively rare, most seem to be a (presumably) cheaper design where the hole has been cut round and small cutouts made at each corner thus only gripping the corners of the bleed screw and doubtless failing like this

However I think this looks like it has the right shape hole, ie square.  

 

 


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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 AgentGeorge
(@agentgeorge)
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09/11/2025 9:49 am  

@adamk these are called roll top rads, they were still available at screwfix till few years ago in their budget range.

The bleed keys are not strong, ive had to use a pair of pliers on the tab of the key to gently persuade them to budge, apply some wd40 and leave for a while if they're too stiff to move.

On one rad I had to grind down the end of the roll top slightly to get a wrench in and give it a good smack.

Failing that, its a new rad



   
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 AdamK
(@adamk)
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Topic starter 12/11/2025 10:07 pm  

@agentgeorge this is a pic of the bleed valve that’s snapped. It should have a square bleed pin in the centre of that sort of nut insert.

IMG 1241


   
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 AgentGeorge
(@agentgeorge)
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Posts: 149
13/11/2025 7:54 am  

The double panel radiators I’ve seen have a bleed screw on both panels.

Usually the nut around the bleed screw can undo allowing it to be replaced.

Id take the photo to City Plumbing and show them if they have spare parts for your style of radiator.

Alternative is to lock of the radiator valves for safety reasons, get a dremel and grind a groove in the bleed screw, then use an impact hammer with a slotted bit and hammer it free.

use WD40 on the bleed screw if it doesn’t budge and try again later. I’ve also used a blow torch on it to cause it to expand and crack the stuck thread.

If you can find a scrap radiator, you can obtain the replacement bleed screw, watch out for those trucks that go round collecting scrap metal, they’ve always got radiators on them; ask nicely and you get them to give you one



   
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 AdamK
(@adamk)
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Topic starter 13/11/2025 10:01 pm  

@agentgeorge it has got 2, the other bleed screw is the other end.



   
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