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Rodents! A word of warning for heat pump owners

 
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Air Source Heat Pumps (ASHPs)
Last Post by Transparent 2 days ago
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 Tim441
(@tim441)
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Joined: 3 years ago
Posts: 375
Topic starter 29/08/2025 6:01 am  

just thinking about how a mouse got in the hole on the bottom of heat pump. I'm guessing that leaves building up on the drip tray helped give it a platform to climb on? Something to keep cleared.


Listed Grade 2 building with large modern extension.
LG Therma V 16kw ASHP
Underfloor heating + Rads
8kw pv solar
3 x 8.2kw GivEnergy batteries
1 x GivEnergy Gen1 hybrid 5.0kw inverter
Manual changeover EPS
MG4 EV


   
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Toodles
 Toodles
(@toodles)
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29/08/2025 8:17 am  

@tim441 As an annual event, I used to record the Christmas Service for a local Private School. One Christmas week, I arrived at the chapel and started to set up all the audio equipment and then plugged into the main …. no power! Upon investigation we found the fried culprit with its’ teeth still engaged with the lead sheathing of the mains wiring. (The chapel rarely had need of electrical power as they still used candles for all ceremonies; power was run from a nearby Master’s House and I was set up in time for the proceedings.) Regards, Toodles.


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


   
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 JamesPa
(@jamespa)
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29/08/2025 8:38 am  

Wasps caused frequent tripping of my lighting circuit a few years ago.  A fair amount of ceiling was removed to find a joint block in which several had met their maker.


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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 Lucia
(@lucia)
Prominent Member Member
Joined: 2 years ago
Posts: 354
02/09/2025 9:17 am  

@tim441 I will need to give some thought to protect the hole with mesh.... perhaps expanding mesh used by builders. Either galvanised or stainless

Just an fyi but steel wool washing up pads are very effective at keeping those critturs out.  This is tried and tested. I buy multi packs and pull them apart.  🐭😁



   
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Toodles
 Toodles
(@toodles)
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02/09/2025 1:43 pm  

@lucia One look at that protection and the rodents will make a clean getaway 😉.


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


   
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Mars
 Mars
(@editor)
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29/09/2025 10:10 am  

I'd be curious to know if anyone else on the forums (other than Tim obviously) has inspected their heat pump unit to check for rodent activity and/or damage, and whether you've taken any preventative measures to seal potential access points.

It's interesting to see that manufacturers and installers don't really take this into consideration.


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Toodles
 Toodles
(@toodles)
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29/09/2025 10:33 am  

@editor Manufacturers should surely be designing out any possible points of rodent ingress so that there is no need, for as we all now know many installers / service agents do not even unscrew the casing once installation has been completed! (Not the good ones I don’t mean @ashp-bobba, the likes of yourselves are the exception of course!) Regards, Toodles.


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


   
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 ASHP-BOBBA
(@ashp-bobba)
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29/09/2025 5:10 pm  

I did notice that if they want to get in they will, they seem to be able to even chew through light steel and plastic casings as well as the gaps round the back, as I said before we get one or 2 a year where a mouse or some kind of small rodent made a nest and blew up the main PCB. If I was to estimate I would say its one in 500 systems we take care of have this problem maybe slightly less so not on the radar of manufacturers during warranty so not their problem probably.


AAC Group Ltd covering the Kent Area for design, supply and installation of ASHP systems, service and maintenance, diagnostics and repairs.
Professional installer. Book a one-to-one consultation for pre- and post-installation advice, troubleshooting and system optimisation.


   
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 Lucia
(@lucia)
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29/09/2025 7:54 pm  

Posted by: @editor
↑

I'd be curious to know if anyone else on the forums (other than Tim obviously) has inspected their heat pump unit to check for rodent activity and/or damage, and whether you've taken any preventative measures to seal potential access points.

It's interesting to see that manufacturers and installers don't really take this into consideration.

I have the 🐙 annual service on Friday so will specifically ask for rodent inspection (seeing as I live rurally). Hopefully not.

However, they loved eating the spare piece of lagging in my cellar last year where the tank is. So I now have a new door threshold, a brush strip on the door and the steel wool mentioned above, on any gaps.

I have a fresh piece of lagging on the cellar floor as a 'mouse monitor' and so far.... no bites. 🤞🏻

 



   
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Mars
 Mars
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29/09/2025 8:53 pm  

@lucia, I hear you on the lagging and insulation front. What I find interesting is the amount of holes and gaps that exist in the chassis that allow these critters easy access. 

chewed insulation

 


This post was modified 3 months ago 2 times by Mars

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Transparent
 Transparent
(@transparent)
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30/09/2025 10:33 am  

I think similar care should be taken against vermin ingress when running pipes and cabling through external walls.

There needs to be 'material' which fills the gap between the insulated pipes and the outer sleeve which prevents the wall bearing on those pipes.

If the entry point is below the DPC (damp-proof course), then the sleeve is generally filled with gravel (10mm).
That would apply to GSHPs in particular.

The majority of entry points will be above DPC.
Steel wool and expanding foam spray are commonly used, but

  • expanding foam isn't UV-resistant and needs over-painting with bitumastic paint/jelly where it's visible to the outside.
  • vermin could still chew through spray-foam over time; use a piece of aluminium-mesh as sold for car body repairs to seal the exterior against anything bigger than an ant!

 


This post was modified 3 months ago by Transparent

Save energy... recycle electrons!


   
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Mars
 Mars
(@editor)
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Joined: 5 years ago
Posts: 3891
19/10/2025 12:44 pm  

Inspired by the original post from @tim441, here's a short video on mice, rodents and heat pumps:


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