TL;DR
A cold trap means no steam is reaching it. Check the upstream isolation valve first, then the inlet strainer. A cold trap with upstream steam and no isolation valve closed is a failed-closed trap or a plugged strainer.
What you might see
- trap inlet and outlet both at ambient temperature
- no condensate discharge observed
- upstream equipment cold and not heating to setpoint
- adjacent traps in the system operating normally
Likely causes
Upstream isolation valve closed or partially closed restricting steam supply to the trap
Inlet strainer completely plugged with scale or debris blocking steam and condensate flow
Steam supply to this branch of the distribution system shut off by another valve upstream
Failed-closed trap internals (see the waterlogging procedure on this machine)
Required tools
- IR thermometer
- LOTO kit and isolation valves
- Heat-resistant gloves
- Strainer cleaning tool or spare screen
Safety first
- Wear heat-resistant gloves when opening the strainer cover, even when the trap appears cold. Trapped steam or condensate can cause burns.
- When restoring steam to a cold line, open the isolation valve slowly to avoid water hammer from condensate that has accumulated in the cold piping.
Procedure
- 1
Verify the upstream isolation valve is fully open. This is the most common cause of a cold trap, especially after maintenance.
- 2
Trace the steam supply line back from the cold trap to the nearest junction. Confirm that all isolation valves in the supply path are open.
- 3
Use an IR thermometer to check the temperature upstream of the trap. If the upstream pipe is also cold, the steam supply is off.
- 4
If the upstream pipe is hot but the trap is cold, the inlet strainer or the trap internals are blocked. Isolate the trap and inspect the strainer.[1]
- 5
Remove and clean the strainer screen. Reinstall and open the isolation valve. Check whether the trap is now receiving steam and cycling.
Warning: Even after isolation, residual pressure and hot condensate remain in the strainer and trap body. Open the strainer cover slowly and wear heat-resistant gloves. - 6
If the strainer is clean and the trap remains cold with steam supply confirmed, follow the waterlogging-failed-closed procedure on this machine.[1]
Sources
Armstrong 800 Series Inverted Bucket Steam Trap Installation and Maintenance, Armstrong International
Armstrong International 800 Series Steam Trap Installation and Maintenance Instructions, trap inspection and strainer maintenance (general)
View source
More guides for Armstrong International 800 Series
How to diagnose continuous discharge on an Armstrong 800 steam trap
An Armstrong 800 inverted-bucket trap at full condensate load will discharge nearly continuously. Distinguish normal operation from a fault by checking with an ultrasonic tester: continuous high-frequency noise means steam loss; intermittent modulated noise at high rate is normal condensate discharge.
How to fix steam loss from a failed-open Armstrong 800 steam trap
A failed-open trap is blowing live steam continuously. Confirm with an ultrasonic tester, then isolate and replace the trap internals (the Armstrong 800 has a replaceable bucket module). Leaving a blown trap in service wastes significant energy.
How to fix waterlogging from a failed-closed Armstrong 800 steam trap
A failed-closed trap does not discharge condensate, causing waterlogging upstream. Test with an IR thermometer: the trap inlet will be cold. Isolate, clear the strainer, and replace the trap internals if the strainer is clean.
Stop fixing the same fault twice.
Dovient turns guides like this into your team's shared playbook, with AI that catches recurring issues before they break the line.