Condensate gurgling sounds in Zehnder Comfoair

[Peter Thompson]

Zehnder have been helpful in diagnosing a sound that we first put down to worn bearings or wind noise from the external baffles.  But when they realised that I had relied on its very tight push-fit, and hadn't solvent-welded the overflow pipe, they pointed out that the noise was air being sucked in the joints by a negative pressure in the condensate sump of the unit.

They were half right, in that air was being sucked in. The condensate was drained to one of the inlet spigots of the standard water-trap of the utility sink.  From the guidance, as this sink is in regular use it fulfilled Zehnder's requirements. However, because the sink obviously has a main drain hole and an overflow, until both of these were sealed, air could always be drawn back to the MVHR unit.

This shows that the MVHR needs either its own, dedicated water trap, or that a waterless, non-return valve is essential.....I will be fitting one. I have suggested to Zehnder that perhaps they should explain this in their instructions, but I guess they assume that it will always be professionals that fit these things.

Anyway, this might be useful information to anyone else fitting their own system or who is having this problem.

 

Edited 6 hours ago by Peter Thompson
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[Nick Laslett]

Two useful videos here for anybody interested in more details on the Zehnder condensate requirements. 
 

 

 

[Mike]

1 hour ago, Peter Thompson said:

This shows that the MVHR needs either its own, dedicated water trap, or that a waterless, non-return valve is essential.....I will be fitting one. I have suggested to Zehnder that perhaps they should explain this in their instructions

You're right; it is standard practice to use a non-return or waterless trap for the reason you mention, but Zehnder's instructions sometimes suggest otherwise. For example they require only a U-bend with water seal in the CA 200 manual, but a non-return trap on my more recent CA 225 model.

 

Avoid a dedicated water trap as it's likely to dry out.

 

50 minutes ago, Nick Laslett said:

Two useful videos here for anybody interested in more details on the Zehnder condensate requirements

A good illustration of the principle, although my CA 225 has a 20mm drain so requires an alternative pipe adapter. A hole drilled through a rubber bung is doing fine so far.