How to Perform a Stage Coil Test
Stage Coil Test your Constant Humidity Controller Gas Burner
This page explains how to perform a stage coil test. If your Constant Humidity Controller (CHC) gas burner is not reaching full flame or is behaving inconsistently, the stage solenoids may be at fault. This guide explains how to do a stage coil test quickly and safely.
What Are the Stage Solenoids?
The CHC gas burner uses three solenoid coils to control the staged flame levels. These are:
- L - Low flame stage
- M - Medium flame stage
- H - High flame stage
When working correctly, each coil becomes magnetised during operation. A coil that fails to magnetise indicates either a failed coil or a blown fuse.
What You'll Need For a Stage Coil Test
- A small non-magnetic metal object (important — a magnetic screwdriver, for example, is not suitable as it will give a false reading)
- Access to the burner control panel
Step 1 — Locate the Solenoid Coils
The three solenoid coils (L, M and H) are located on the burner unit itself.
Step 2 — Put the Burner Into Full Flame Mode
To energise all three solenoid coils simultaneously, the burner must be running at full flame. How you achieve this depends on your current operating mode:
- RH Mode — Set the target humidity to its lowest setting
- Temperature Mode — Set the target temperature to its highest setting
Allow the burner to ignite and attempt to reach full flame before proceeding.
Step 3 — Locate the Coils Up Close
Once the burner is running at full flame, carefully approach the solenoid coils.
Step 4 — Test Each Coil for Magnetisation
With the burner running, touch your non-magnetic metal object directly onto the metal nut on top of each coil in turn — L, M, and then H.
- Attracted to the nut — the coil is working correctly and is magnetised
- No attraction — the coil or its associated fuse has failed
Work through each coil methodically and note which, if any, fail to attract the metal object.
Step 5 — Diagnose the Fault
If a coil shows no magnetisation, there are two likely causes:
Blown fuse — check and replace the fuse associated with that stage first, as this is the simplest fix
Failed coil — if replacing the fuse doesn't resolve the issue, the coil itself may need replacing
Need Further Assistance?
If you're unable to resolve the fault after testing, please don't hesitate to contact the Harvest Installations team. You can reach us by phone on +44 (0)1284 762451 or by email at info@harvestinstallations.co.uk and we'll be happy to help.