We got an offer from Lier Everk to get a service agreement for our Panasonic CS-CE7GK air-to-air heat pump. For NOK 1200,- (about $200) they would come and clean our heat pump every 2nd year. I did some research and it looks like you easy can do this yourself.
The first part is to clean the coils of the unit. Turn off the power of the unit. Remove the filter. Vacuum any dust that can be seen. Use luke varm water and dishwasher liquid (Zalo) and just spray your indoor coils. Use a towel to collect excess water dripping from the unit. The outdoor unit is cleaned the same way. Spray on. Wait for a while for the dish washer liquid to disolve dirt. Then use a garden hose with low pressure and apply water in the opposit direction of the normal airflow. Be careful not to bend any coil fins. Let the unit sit for some hours to dry before turning on power.
The second part is to check that it still delivers the heat (or cold) that it should. According to the Pabasonic service manual the difference should be at least 14 C in heat mode and at least 8 C in cooling mode. I checked ours by setting the temp to 27 C. Inlet temp showed 23C and outlet 42C. A difference of 19C (The unit using 484W). Then for fun I set the additional "Powerful" mode. Inlet temp is then 23 C and out take 48 C. (The unit using 985W). A differance of 25 C. Outdoor temperature was 13 C. If the temperature difference is less than 14C you should check that all coils are clean. If cleaning does not help, it is time to call for service.
Summary in Norwegian:
Du kan enkelt rengjøre din varmepumpe selv. Vask ved å spraye på med lunkent Zalo-vann. Utdelen kan i tillegg spyles med hageslange med lavt trykk, aluminiums finnene må ikke bøyes. Det skal være en temperatur forskjell på minst 14 grader mellom luft som går inn i inndelen og luft som kommer ut av den ved normal drift.