When checking the contacts in a thermostat, what indicates that it needs to be replaced?

When assessing the condition of the contacts in a thermostat, the key indicator that replacement is necessary is if the contacts are cratered out, worn very thin, or welded together.

Cratered contacts suggest severe erosion due to the continuous opening and closing cycles that the thermostat undergoes, which can lead to poor electrical connections and prevent proper operation. If the contacts are worn very thin, they may not be able to adequately conduct electricity, which compromises the performance of the thermostat and can lead to temperature control issues. Additionally, if contacts are welded together, it indicates a serious malfunction where they cannot separate, leading to continuous power flow and potential overheating or equipment damage.

These conditions directly impact the reliability and efficiency of the thermostat, resulting in the need for replacement. In contrast, dusty contacts, stained but intact contacts, or contacts covered with grease may point to neglect or surface contamination but do not indicate the extreme mechanical failure or operational failure represented by cratered or welded contacts.