My wife and I purchased a Bosch SM036 Geothermal unit back in late September. It replaced a 29 year old unit. The first six-7 weeks the unit was actually perfect. Very quite, efficient and we felt very good about the purchase. Then we had an issue with the thermostat and had to have it replaced. Now the unit is much louder, we hear the bang of the compressor that we heard with the previous unit. The installer, who we like very much, put in a device to regulate the water flow. That seemed to help a little but the noise is still there. When I review the information on the Bosch units one of the features they list is how quite it is. The noise level is loud enough that it is effecting sleep. Appreciate any suggestions.

Open loop or closed loop?

Open loop. Thanks.

typically the noise is from turbulence in the water flow due to the regulating valve. if that was adjusted or added at the same time as the problem surfacing, then it is the place to look. since you mention the thermastat only, it could be set or installed so that you are getting a 2nd stage call (your heat pump is 2-stage and the 2nd stage could be a little louder).

Thank you for the response. It does indeed seem to be a water flow issue. Our installer made some adjustments with the piping and it is much better now.