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Vaillant aroTHERM plus not level or flat - what base is best under an external unit?
Hi. I've had a Vaillant aroTHERM plus installed. The external unit has installed on some existing flagging behind next my house in my garden. The flagging wasn't level, so the installer has used some flint from my garden to raise one side of the unit by a 15mm or so
The installer checked the unit was level using a spirit level (I saw them take a photo of it). But I've since checked with a laser level and the external unit is not level and the top is also not flat, one corner is lower than the rest. I think the top of the unit not being flat has made the installer think it is level when it actually isn't. One corner is about 5mm to low and another is 10mm to low
I was wondering, how to installers normally handle installing an external unit on existing flagging that isn't level? I'm thinking of getting some flagging relayed to go under it. Is flagging the best thing for an external unit to be placed on or would a concrete base be better? Are the any requirements for what it is installed on, e.g. does some of it need to be drainage rather than a firm base? E.g. is it better for all the base under the unit to be solid or just have a solid base under each foot
I had thought that my installers would mount straight onto the existing paving slabs but no, they lifted slabs, cut to fit the area they needed and mounted the ‘curb stones’ you see in the photo in a frame they made. They bedded the stones into sand and levelled them before adding the drainage stones you see. I’m not sure how much depth of sand was used but none of the condensate has ever appeared on the paving in front of the pump but is well contained within the wooden framed base area. Regards, Toodles.
Toodles, heats his home with cold draughts and cooks food with magnets.
@diymax welcome to the forums. There's a new product on the market called Zeus mounting feet. See attached. Would you like me to connect you with them?
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@diymax will do. I'll send an email to their team and cc you using the email address you used to register on this forums. I'll do that tomorrow morning.
New to heat pumps? Take the Heat Pump Fundamentals course and use INTRO50 at checkout for 50% off.
Rewritten and updated for 2027
📘 From Zero to Heat Pump Hero
🛠️ Bodge Buster
🎧 Prefer to listen? Heat Pumps Explained
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