All About Heaters

At first glance, a residential strip heat kit could look intimidating. I want to break down the operation and troubleshooting in a way that should give you confidence. Be careful and keep safety in mind while performing the tasks mentioned in this article because the power will have to be on to make these checks. Although different brands will look slightly different, the concept and troubleshooting will be the same.

Here are the different parts of a double (10kw) heat kit:

1. High voltage terminal block
2. DC Heater relay with an AC to DC rectifier attached
3. High temp auto resettable limit
4. High temp fusible link
5. Electric heater

Okay, let’s break this heater down even further and discuss each of the 5 different parts in depth for proper operational checks when a heater kit isn’t working:

1. High voltage terminal block:

The terminals should read the rating voltage displayed on the heater at all times. In this example the kit is rated for 230v. It is common for heat kits to have a separate power source and this voltage should be confirmed to ensure a breaker wasn’t tripped.

2. DC Heater relay with an AC to DC rectifier attached:

-LOW VOLTAGE-This heater relay consists of two parts, the actual relay and a rectifier. Notice the voltage on this relay is 28vdc. Some relays can be 22vdc.

Verify that the rectifier is receiving 24vac. Once this has been proven, the rectifier can be removed to confirm proper output voltage. In this example, the output is reading 33vdc. If the voltage output were to be zero, then it would indicate a faulty rectifier. When the relay receives the correct voltage, the relay should close its contacts.

-HIGH VOLTAGE- These relays consist of two set of contacts. One set is located on the top left of the relay and another on the top right. When the relay doesn’t have proper low voltage to energize the coil or if the coil is faulty, the contacts will read 240vac. If the relays close correctly with applied low voltage, then the contacts will show 0vac when checked in this manner:

3. High temp auto resettable limit:

This limit, like many other limits, is displaying its tripping and resetting temperatures. This information can be used when selecting a universal limit or when troubleshooting if the limit is opening/ closing at the right temps. The resettable limit and the fusible link test and function in the same manner EXCEPT that the limit will reset itself and the fusible link cannot. Troubleshooting and operation for this limit will be under #4 fusible links.

4. High temp fusible link:

Fusible links are the “backup limit” for when the resettable limit fails or the heater draws too many amps. They typically have a melt/open point of around 300F. Here are the two most common fusible links: The link that is wire only will actually melt and therefore open the power circuit physically and can be seen but, the link that has a device on the wire will internally open and will not alter its look when tripped.

If a limit or fusible link is suspected for a heater not functioning, then simply check the voltage with a meter to ensure that the voltage drop across it is 0vac in the same manner as the contacts were checked on the relay. If a meter were to read 240v, then the limit is open/ or the fusible link has been melted/opened.

5. Electric heater

The electric heater is the star of the show and the easiest to check. This is the meeting place for both 120vac power legs and SHOULD read 240vac. If your meter reflects the heater has 240vac but the current (amps) is zero (assuming the amp clamp is accurate) then this would indicate the heater has failed and is “electrically open” and should be replaced. The meter leads should be placed in this manner for this test:

Keep in mind that parts do fail from simple wear and tear from normal usage, but repeated failures usually happen for a reason and these repeated failures should be investigated further to find the root cause.