Maybe the small heating water tank or the heating water pipe is blocked. At idle speed, slow water flow will hinder circulation. Only by increasing the speed and water flow can there be fever, which may be due to improper use of antifreeze and impurities in the cooling system. If it is a problem with the water tank, it is better to replace it, and the cleaning effect is not ideal. If it is a water pipe, the maintenance plan depends on the situation.
Check the thermostat and warm water valve and replace them if necessary. Check whether the warm water tank is blocked, and replace it if it is blocked.
If the water temperature is low, check the thermostat; If the water temperature is normal, check whether the radiator pipe of the heater is blocked.