Thema "low flow on heating H1 and DHW" in Wärmepumpe & Hybridsysteme

low flow on heating H1 and DHW

Jeroen_VR — Thu, 13 Nov 2025 09:47:38 GMT

It is our first heating of the season.

Our domestic hot water has run from June till now without any issues, flow rates were higher than now. After switching on the HK1 on 24th of october, the flow was ok. On 26th, there was a strange curve (see attached).

Since then, the flow rate has dropped significantly for both HW and DHW.

Currently, on DHW, the flow is around 214l/h to heat up a 200 l buffer (vitocell 100-V).

Setting for DHW pump: 60%, but only runs at 10% according to the display.

For heating all underfloor heating: 96 m² downstairs on a 9 loop manifold, all acuatators fully open and 13m² upstairs (bathroom) directly connected to main flow and return.

Flow only reaches 300-340 l/h, way too low for this heating system. The flow was higher before and has consistently dropped. Setting is 90%, but only reaches around 11% pump speed. There is some noise at the indoor unit. Additionally, we saw some water in the indoor unit (on the left (top and bottom).

What could be the cause? Our heating engeneer will come together with the viessmann expert next week to check.

Any tips or recommendations to check?

Re: low flow on heating H1 and DHW

Flo_Schneider — Fri, 14 Nov 2025 10:38:17 GMT

Hello Jeroen_VR,

Which heat pump model do you have?

Best regards
Flo

Re: low flow on heating H1 and DHW

Jeroen_VR — Fri, 14 Nov 2025 10:45:19 GMT

Hi Flo,

Please find a picture of the system. Could it be that the ball valve with arrow pointing downwards is in the wrong direction?

S/N number is in my profile details.

Thank you.

Re: low flow on heating H1 and DHW

Flo_Schneider — Fri, 14 Nov 2025 11:07:36 GMT

Sorry, your signature is not visible in my program, otherwise I would have been able to see it.

Is water constantly leaking from the indoor unit?

Otherwise, I recommend cleaning the filter screen on the outdoor unit. It may be clogged, causing insufficient circulation.

Best regards
Flo

Re: low flow on heating H1 and DHW

Jeroen_VR — Fri, 14 Nov 2025 11:18:07 GMT

S/N: 7994218412569124

Re: low flow on heating H1 and DHW

Jeroen_VR — Fri, 14 Nov 2025 11:19:13 GMT

S/N: 7736172159632221

Re: low flow on heating H1 and DHW

Jeroen_VR — Fri, 14 Nov 2025 11:21:23 GMT

The water is not leaking from the indoor unit constantly. Pressure also remains stable.

Next week, the viessmann expert and our heating engineer will come over to check everything.

Any other tips?

I also suspect a wrongly installed ball valve (see picture with flow direction arrow pointing downwards now).

Re: low flow on heating H1 and DHW

Flo_Schneider — Fri, 14 Nov 2025 11:38:20 GMT

I can't confirm that from a distance. In any case, the easiest thing to do is to check the filter first.

Best regards
Flo

Betreff: low flow on heating H1 and DHW

Küstenpumpe — Fri, 14 Nov 2025 11:50:59 GMT

Did you checked the Filter same as the Youtube Video ?

Betreff: low flow on heating H1 and DHW

Jeroen_VR — Sat, 15 Nov 2025 10:01:03 GMT

It was indeed a very dirty filter.

Flow is now normal at 1077 l/h during heating.

In will have to check more regular, did not expect this from a fully new installation.

Thank you!

Re: Betreff: low flow on heating H1 and DHW

Flo_Schneider — Mon, 17 Nov 2025 07:21:38 GMT

Thanks for the info, and I'm glad the cause was found. Even with a new pipe installation, there can be dirt in the pipes.

Best regards
Flo