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

N
Nicholas GarciaSep 12, 2025
What to do if my HTP Boiler experiences a blocked vent pressure switch?
- B
  Brandon BrownSep 12, 2025
  If you're experiencing a blocked vent pressure switch on your HTP Boiler, first check the flue vent to ensure it is not blocked or damaged. Then, check the switch wiring by applying a jumper in place of the switch. If the code clears with the jumper in place, replace the flue switch and connect the wires to the new switch before running the boiler. Warning: Do not use a jumper to remedy this error; faulty switches must be replaced. Failure to do so could result in serious injury or death.
A
Angela EllisSep 13, 2025
What to do if my HTP Mod Con 300 HL Boiler has low water flow (for users with optional flow switch only)?
- E
  Eddie RodriguezSep 14, 2025
  If you have an HTP Boiler with an optional flow switch and are experiencing low water flow, first check to see if the boiler circulator is functioning correctly and repair if necessary. Next, ensure water is flowing in the system by checking for valves that should be open and looking for plugged filter screens. Finally, check the flow switch and its wiring, repairing as needed.
K
karenbryantSep 15, 2025
What to do if my HTP Mod Con 300 HL's line voltage frequency is out of range?
- F
  francisco96Sep 16, 2025
  If your HTP Boiler's line voltage frequency is out of range, inspect the power wiring to the appliance and repair as necessary. If connected to line voltage, notify the power company. If connected to an alternate power source, such as a generator or inverter, make sure the line voltage frequency supplied by the device is 60 Hz.
W
wbrownSep 18, 2025
What to do if the outside sensor is shorted or the temperature is less than -40 degrees F on my HTP Mod Con 300 HL Boiler?
- D
  dianasextonSep 18, 2025
  If the outside sensor on your HTP Boiler is shorted or the temperature reading is less than -40 degrees F, inspect the wiring from the outside sensor for damage or shorted connections and repair as necessary. Measure the resistance of the outdoor sensor and compare it to the resistance chart. If it's not within the range of the chart, or if it's shorted or open, replace the sensor.
S
Stephen KaufmanNov 25, 2025
What to do if the HTP Mod Con 300 HL Boiler shows 24 Volt Low?
- B
  Brandon OwensNov 25, 2025
  If your HTP Boiler indicates '24 Volt Low', start by checking the line voltage, ensuring it's between 100 – 128 volts. If available, connect a PC and, using HTP service software, check the 24v supply display in the lower left corner of the screen. The number displayed here must be greater than 128 and should be greater than 250. Remove the 10 pin Molex connector from the customer connection board. If LOU clears, then the problem is with external sensor wiring. Examine external sensor wiring for shorts to ground, repairing as necessary. If LOU code is still present and the heater is so equipped, disconnect high gas pressure switch, then low gas pressure switch, then UL 353 low water cutoff in this order, one at a time, to see if LOU code clears. Replace faulty part. Check low voltage wire h...

HTP Mod Con 300 HL Specifications

General

Brand	HTP
Model	Mod Con 300 HL
Category	Boiler
Language	English

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