ᐅ Clicking noises in the circulation system during thermal stagnation

Dear house building forum members,

I operate a heat pump system (Buderus WPS-10, geothermal) with a storage tank and solar thermal support (2 x Braas TK8) in our single-family house.

In summer, when the sun is very strong and the system reaches thermal stagnation—meaning the circulation pump switches off—there are continuous ticking noises somewhere in the attic, around where the connections between the solar collector module hoses and those leading to the storage tank in the basement are located. The noise sounds as if someone has hidden a clock behind the drywall of the roof.

I reported this issue to the heating engineer as a defect and suggested that cavitation might be occurring there, expressing concern that this could cause material wear over time.

After the service technician finally experienced the effect live (sunshine required), he adjusted the target or limit/alarm settings of the system. As a result, every day when the sun was shining, the heat pump triggered an alarm due to limit exceedance, causing a buzzer in the basement, and the alarm had to be acknowledged daily.

At times, I manually removed the heat stored in the collectors at night by setting the controller to manual mode in the evening and switching on the pump. However, this is very inconvenient, so I reset the limit values again, which brought back the ticking noise.

Repeated calls and an email to the heat pump manufacturer (Buderus) were completely useless—just as well I could have asked my grandmother. It seems the people there are only assigned to answer phone calls without any technical expertise.

I actually have a not-too-bad relationship with the heating engineer, but I fear this issue exceeds his competence as well. At any rate, he is very reserved on the matter and far from proactive.

Therefore, my question to you in this forum: Has anyone ever experienced or heard of this phenomenon and possibly knows how to deal with it?

The system in the basement operates at about 2.5 bar (36 psi) at rest, thermal stagnation begins at around 150°C (302°F), pressure rises to about 4.5 bar (65 psi), and temperature reaches a maximum of 190°C (374°F).

Thank you very much and best regards,
Thorsten

This is a very specific and technical question, so I would definitely bring it up in the "Rosa" forum. Heating system installers and others are active there.

Thorsten63 schrieb:

Dear housebuilding forum members,

I operate a heat pump system (Buderus WPS-10, ground source) with a storage tank and solar thermal support (2 x Braas TK8) in our single-family home.

In summer, when the sun shines very strongly and the system reaches thermal stagnation (meaning the circulation pump switches off), persistent ticking noises occur in the attic, somewhere near the connection of the solar collector module hoses to those running down to the storage in the basement. It sounds as if someone hid an alarm clock behind the drywall of the roof.

I reported this issue as a defect to the heating installer and suspected cavitation was happening there. I was also concerned that this could cause material wear over time.

After the service technician was finally able to experience the effect live (sunlight required), he adjusted the target and limit/alarm values of the system. As a result, every sunny day triggered an alarm at the heat pump, causing beeping in the basement daily, and the alarm had to be acknowledged.

At times, I manually ran the heat away at night through the collectors by setting the controller to manual in the evening and switching the pump on. This is very inconvenient, so I reverted the limit values back, which brought the ticking noise back.

A repeated call and an email to the heat pump manufacturer (Buderus) were completely useless – I might as well have asked my grandma. Apparently, these people are only there to take calls without any technical expertise.

I generally have a fairly good relationship with the heating installer, but I fear this issue might be beyond his expertise as well. He is very reserved on the subject and far from proactive.

Therefore, my question to you here in the forum: Has anyone experienced this phenomenon themselves or heard of it and possibly knows what can be done about it?

The system pressure in the basement is about 2.5 bar (36 psi), thermal stagnation begins at around 150°C (302°F), then pressure rises to about 4.5 bar (65 psi), and temperature reaches a maximum of 190°C (374°F).

Many thanks and best regards,
Thorsten

We had a similar issue where the supply and return lines to the underfloor heating from the heat pump were swapped.

KingJulien schrieb:

This is a very specific and technical question. I would definitely bring it up in the "Rosa" Fo..., where heating system installers are active among others.

Hello KingJulien,
thanks for the tip!
Best regards
Thorsten

Offtopic schrieb:

We had a similar issue where the supply and return lines to the underfloor heating, coming from the heat pump, were reversed.

Hello Offtopic,
thank you for your input. That’s quite interesting! I will definitely look into it further. Mistakes like that can easily happen to a professional technician. In our case, the toilet was connected to the hot water supply, which meant it always flushed warm, and condensation dripped from the cistern. We had to remove a tile and switch the connection — problem solved quickly! If it’s as easy to fix here, that would be great already. One question though: what does “wgt” mean?
Best regards
Thorsten

Thorsten63 schrieb:

Hello Offtopic,
thank you for your contribution. That’s fascinating! I’ll definitely follow up on this. Something like that can easily happen to a professional tradesperson. In our case, the toilet was also connected to hot water, which meant it always flushed with warm water, and condensation dripped from the cistern. We had to break open the tile and replace the connection, and just like that, the problem was solved! If it were this simple here, that would already be a big step forward! One question: what does “wgt” mean?
Best regards,
Thorsten

Wgt stands for controlled residential ventilation, which includes a heat exchanger to preheat the fresh air after heat recovery to avoid drafts.