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Glycol

Air Source Heat Pumps (ASHPs)

Last Post by Transparent 2 months ago

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Westkent

(@westkent)

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Joined: 2 years ago

Posts: 61

Topic starter 01/10/2025 4:11 pm

Hi all. Quick question.

A quick easy way to determine if my system uses Glycol would be to check the colour of the liquid. Is this correct??

My landlord is stating the system won’t require a glycol flush as there’s anti freeze valves fitted.

Im not so sure so just wanted to check.

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Old_Scientist

(@old_scientist)

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01/10/2025 6:44 pm

Glycol is colourless, but typically glycol sold in the UK for use in heating systems has a light blue colouration. If you empty the contents of your Y strainer into a white container, you should be able to see the pale blue colouration if glycol is present.

Samsung 12kW gen6 ASHP with 50L volumiser and all new large radiators. 7.2kWp solar (south facing), Tesla PW3 (13.5kW)
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JamesPa

(@jamespa)

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01/10/2025 7:39 pm

Posted by: @westkent

↑

My landlord is stating the system won’t require a glycol flush as there’s anti freeze valves fitted.

Im not so sure so just wanted to check.

If there are indeed antifreeze valves you dont need glycol. Look for these outside near the heat pump, only just protruding from the insulation. Some argue that you dont need a/f valves either (did anyone fit a/f valves or glycol to outside oil boilers - no!)

This post was modified 2 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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ASHP-BOBBA

(@ashp-bobba)

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01/10/2025 9:03 pm

You need a refractor to know if you need attention to your glycol, if you have ant-freeze valves you will not have glycol.

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Mars

(@editor)

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01/10/2025 9:22 pm

@ashp-bobba, given the installation quality we see from many installers, I honestly wouldn’t put it past some of them to fill a system with glycol and then stick AF valves in as well.

I’ve had conversations with plenty of installers who weren’t even aware of the detrimental effects glycol can have on heating systems. The increased viscosity alone means higher pumping energy, reduced flow rates and greater wear on components, so if someone bodges it in without thinking, the system performance takes a real hit. Sadly, it really wouldn’t surprise me if some guys out there have done exactly that…

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Mars

(@editor)

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01/10/2025 9:26 pm

@westkent, glycol has a very distinct smell. I’ve spent the day smelling it myself while trying to de-air our system. If you’ve got a filter you can isolate, drain a little water and you’ll pick it up straight away. You’ll probably notice it too if you bleed a rad onto a bit of kitchen towel. It’s a sort of sweet, almost sickly smell… once you’ve clocked it, you won’t mistake it for anything else.

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ASHP-BOBBA

(@ashp-bobba)

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01/10/2025 9:29 pm

@editor Good point, I suppose establish that 1st, work out if you have either or both and then go from there?

👍

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Westkent

(@westkent)

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Joined: 2 years ago

Posts: 61

Topic starter 02/10/2025 6:18 am

Well I have in the past done the bleed screw with a towel and it was 100% coloured (green/blue memory not quite with it)

ill now try to confirm if there’s anti freeze valves before I contact my landlord again

This post was modified 2 months ago by Westkent

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Westkent

(@westkent)

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Posts: 61

Topic starter 02/10/2025 11:17 am

So.. after reporting back to my landlord that I do have Glycol in the system and that there are no anti freeze valves iv was told unless I have an issue there’s nothing to they’ll do.

Heat pumps been in six years without a system flush. Should I be concerned??

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Westkent

(@westkent)

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Posts: 61

Topic starter 08/10/2025 12:23 pm

After a bit of a winge to my landlord they’ve now agreed to flush out the Glycol and install anti freeze valves.

Heres hoping that will push up my COP

👍

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JamesPa

(@jamespa)

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08/10/2025 12:56 pm

Posted by: @westkent

↑

Heres hoping that will push up my COP

This alone might not much, are you operating 24*7 on weather compensation with ft as low as possible consistent with house heated to to a comfortable temp. If not then there is another adjustment to do once glycol flushed.

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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