HTP Mod Con 300 HL - User Manual

HTP Mod Con 300 HL

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120 Braley Rd. P.O. Box 429 East Freetown, MA 02717-0429 www.htproducts.com

LP- 205 REV. 3.18.11

Mod Con

INSTALLATION

START-UP

MAINTENANCE

PARTS

Mod Con Models

300 / 500 / 850

LP / HL / LPHL

This manual must only be used by a qualified heating installer/service technician. Read all

instructions in this manual before installing. Perform steps in the order given. Failure to comply

could result in substantial property damage, severe personal injury, or death.

NOTICE: HTP reserves the right to make product changes or updates without notice and will not be held

liable for typographical errors in literature.

Table of Contents

Questions and Answers

W
wrightstephenAug 20, 2025
What to do if my HTP Mod Con 300 HL Boiler has no flame detected?
- J
  Jamie ChapmanAug 20, 2025
  If your HTP Boiler isn't detecting a flame, here's what you can do: First, watch the igniter through the observation window. If there's no spark, check the spark electrode for the proper ¼” gap. Remove any corrosion from the spark electrode and flame rectifier probe. If there is a spark but no flame, check the gas supply to the boiler. If there is a flame, check the flame sensor. Also, check for any flue blockage or condensate blocks.
Y
yangkeithAug 22, 2025
What to do if the HTP Mod Con 300 HL's high temperature limit is exceeded?
- C
  Christopher BeckAug 22, 2025
  If the high temperature limit is exceeded on your HTP Boiler, you should first check the circulation pump operation. Also, ensure adequate flow through the boiler by checking the status menu to confirm that there is less than a 50°F rise from the return thermistor to the supply thermistor. Check the thermistor reading on the supply thermistor and replace the switch if it's faulty. Finally, disconnect the two wires from the thermostat terminals and connect them together, then press the S4/Reset button. If the fault clears, the problem is outside the boiler.
B
bryan68Aug 25, 2025
What to do if my HTP Boiler has a loss of flame signal?
- C
  Charles WilliamsAug 25, 2025
  If your HTP Boiler is experiencing a loss of flame signal, monitor the gas pressure to the unit while it's operating and make sure that the flame is stable when lit. Check if the green light on the display module is off while the heater is running. If it doesn’t come on or goes off during operation, check the flame signal on the status menu. If the signal reads less than 1 microampere, clean the flame rectifier probe. If the flame rectifier probe continues to read low, replace it. Check the stability of the flame rectification signal; if unstable, you may need to replace the burner gasket.
A
Amanda RichardsonAug 28, 2025
What to do if my HTP Boiler's combustion fan speed is incorrect?
- D
  Diana HernandezAug 28, 2025
  If your HTP Boiler indicates that the combustion fan speed is incorrect, you should check the combustion air fan wiring. Also, check the 24 VAC signal by measuring from any connected safety to ground, as a low voltage situation may cause a “false” error code. If those steps don't resolve the issue, consider replacing the combustion air fan or the control board.
R
Rachel JohnsonAug 30, 2025
What to do if my HTP Boiler has a false flame signal?
- M
  Michael DoughertyAug 30, 2025
  If your HTP Boiler is showing a false flame signal, look into the window. If there is flame, turn the gas off to the unit at the service valve and replace gas valve. If the flame signal is present and there is no flame, replace the flame rectification probe. If the flame signal is not present after turning off the gas supply, check the gas valve electrical connection. Remove the gas valve and check for obstruction in the valve seat or replace the gas valve. Turn the gas on at the service valve after corrective action is taken. Check for condensate backup. Condensate backup can damage the refractory wall. If the wall falls against the rectifier probe, it may conduct the signal to ground, giving a false reading.
K
Kyle HernandezSep 1, 2025
What to do if the water level in my HTP Mod Con 300 HL is low?
- C
  Christine RamosSep 1, 2025
  If the water level in your HTP Boiler is low, you should first check the boiler feed water system to ensure it's supplying make-up water. Next, make sure all air is bled from the system. Check for leaks in the boiler and system piping, repairing as necessary. Finally, inspect the low-level switch and wiring for damage and repair if necessary.
M
Martha BarrettSep 2, 2025
What to do if my HTP Mod Con 300 HL's condensate cup is full?
- L
  Leah ZimmermanSep 2, 2025
  If the condensate cup in your HTP Boiler is full, check the condensate lines for obstructions. Also, check the float switch in the condensate reservoir. Finally, inspect the wiring from the condensate reservoir to the 926 control and repair as necessary.
A
ambercarlsonSep 6, 2025
What to do if my HTP Mod Con 300 HL has an interrupted or shorted supply (outlet) thermistor?
- G
  George TapiaSep 6, 2025
  If your HTP Boiler shows an interrupted or shorted supply (outlet) thermistor, first check the electrical connection to the thermistor and verify 5 VDC by checking in Molex connector. If not 5 VDC, check harness. If harness is OK, replace control. If the connection is okay, replace the thermistor. Note that the boiler will reset automatically.
B
Brandon HobbsSep 8, 2025
What to do if the supply (outlet) temperature sensor on my HTP Mod Con 300 HL Boiler exceeds 230oF?
- G
  Gregg PughSep 8, 2025
  If the supply (outlet) temperature sensor on your HTP Boiler exceeds 230°F, first check the circulation pump operation. Then, ensure adequate flow through the boiler by accessing the status menu and confirming that there is less than a 50°F rise from the return thermistor to the supply thermistor. Check the direction of flow on the boiler circulator. Troubleshoot thermistor.
C
Cynthia WashingtonSep 10, 2025
What to do if my HTP Mod Con 300 HL has a system sensor failure (Cascade Master only)?
- M
  Mrs. Ashley Williams DDSSep 10, 2025
  If your HTP Boiler, configured as a Cascade Master, is showing a system sensor failure, check the wiring to the system sensor and repair as necessary. Also, check the sensor resistance and compare it to the resistance table in the manual; replace the sensor if it's not correct.

HTP Mod Con 300 HL Specifications

General

Brand	HTP
Model	Mod Con 300 HL
Category	Boiler
Language	English

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