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Biocide and Inhibitor

 
Thermostats, Volumisers, Buffer Tanks, TRVs, Pumps, Piping, Valves, Radiators & Controls
Last Post by cathodeRay 9 months ago
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 Renewables345
(@renewables345)
Eminent Member Member
Joined: 1 year ago
Posts: 14
Topic starter 02/01/2026 12:38 pm   [#2700]

Hi all

I’m looking to get some insight on what others are using for biocide and inhibitor in air source heat pump systems. I am focused mainly on systems with AFV's, but could also do with some advice on glycol filled system too.

At the moment, we use R700 and X100, but we’ve seen some concerning press recently regarding these products. I’m particularly interested in:

  • What products you trust for preventing microbial growth in ASHP systems.
  • Recommendations for treating systems that already have spores or microbial contamination.
  • Best practices for preventing these issues from occurring in the first place.

Any advice, product recommendations, or experience you’ve had would be really appreciated!

Thanks in advance.


This topic was modified 9 months ago by Mars

   
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ASHP Biocide AFV
cathodeRay
 cathodeRay
(@cathoderay)
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03/01/2026 12:31 pm  

Can you specify what the 'concerning press' is? It may just be typical media scaremongering.

It is also a good idea to spell out what an abbreviation stands for the first time you use it. AFV? Armoured fighting vehicle? If so, that's a bit over the top for harmless bacteria.   


Midea 14kW (for now...) ASHP heating both building and DHW


   
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Toodles
 Toodles
(@toodles)
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03/01/2026 12:37 pm  

@cathoderay I took it to mean Anti-Freeze Valve.🤨 Regards, Toodles.


Toodles, heats his home with cold draughts and cooks food with magnets.


   
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cathodeRay
 cathodeRay
(@cathoderay)
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03/01/2026 12:40 pm  

Posted by: @toodles
↑

I took it to mean Anti-Freeze Valve

Possibly, given the context, but we don't know for sure. IDDAH to spell things out (it doesn't do any harm).


Midea 14kW (for now...) ASHP heating both building and DHW


   
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Mars
 Mars
(@editor)
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03/01/2026 1:13 pm  

Posted by: @cathoderay
↑

Can you specify what the 'concerning press' is? It may just be typical media scaremongering.

It is also a good idea to spell out what an abbreviation stands for the first time you use it. AFV? Armoured fighting vehicle? If so, that's a bit over the top for harmless bacteria.   

I saw some chatter last year about general environmental impacts of biocides/inhibitors (potential for runoff or long-term aquatic effects if not handled properly when systems are flushed). 

 


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JamesPa
 JamesPa
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03/01/2026 1:24 pm  

One school of thought says put almost nothing in and instead treat only to VDI2035 which is a German standard.  So far as I can see there is a lot to be said for this approach.  My cynical side says that, just like smart external controls, the industry may have developed and promoted products we don't need and never needed.


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)
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Joined: 6 years ago
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03/01/2026 10:53 pm  

@jamespa I share your cynicism.  I do suspect there’s a place for biocide I systems, but fully agree that VDI should be a far greater consideration.


🔥 Britain’s Heat Pump Shitshow
How Installing a Heating System Became a National Nervous Breakdown
Free UK shipping.
📗 Heat Pumps Explained
A Jargon-Free Guide for Homeowners
Rewritten and updated for 2027
📘 From Zero to Heat Pump Hero
🛠️ Bodge Buster
New to heat pumps?
Take the Heat Pump Fundamentals course and use INTRO50 at checkout for 50% off.


   
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 Renewables345
(@renewables345)
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Joined: 1 year ago
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Topic starter 05/01/2026 8:54 am  

@cathoderay It is meant to be Anti-Freeze Valves. When I say concerning it is a bit of an exaggeration, but it is more to say that it isn't adding benefit to the system, and rather causing issue with these "spores". We've seen a lot of systems with strainers filled to the brim with them, and we can't seem to find a strong solution to stop this from happening.



   
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cathodeRay
 cathodeRay
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05/01/2026 9:32 am  

@renewables345 — thank you for the clarification. I'm rather aligned with @jamespa and @editor on this, the biocide products are more likely to be be solutions (sic) in search of a problem than anything useful. Inhibitors on the other hand probably do serve a useful purpose.

You can't normally see 'spores' unless they have somehow grown into something macroscopic. Has anyone looked at the debris in the filters under a microscope?


Midea 14kW (for now...) ASHP heating both building and DHW


   
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