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Laars Heating Systems · Series
The Mini-Therm JX is Laars' non-condensing residential gas-fired hydronic boiler line from 50 to 200 MBTU/h, documented at 84% AFUE — a simpler boiler with no digital display, diagnosed through LED indicators and the troubleshooting tables in its installation manual (Document 1478C).
Series facts
84% AFUE published for the Mini-Therm JX series.
The Mini-Therm JX is the non-condensing end of the Laars residential range: the installation manual describes gas-fired hydronic residential boilers in sizes 50-200 MBTU/h, and the parts sections list six sizes — 50, 75, 100, 125, 150 and 200 — in their model columns. The troubleshooting and parts chapters captured for research (Document 1478C) document natural-gas and propane parts sets with altitude groupings, so both fuels are supported on the same boiler.
There is no digital display on the JX and therefore no numeric error codes. Section 11.C of the manual provides a numbered troubleshooting table running from a boiler pump that will not operate through pilot outage, flame roll-out, lazy yellow-tip flames, insufficient heat, noisy pumps, pounding or knocking, condensing at low water temperature, low pressure or bubbles, relief-valve opening, a lit pilot with burners that will not fire, and short cycling.
Diagnosis is analog: Section 11.D's flow charts walk the technician through the control's indicator lights — the green TEMP ACTIVE LED, the red LOW WATER LED and the yellow HI TEMP and TARGET LEDs, plus the ignition and limit lights. The same chapters publish the gas-pressure checks used in diagnosis, including 5.5 to 10.5 in WC inlet on natural gas and 10 to 13 in WC on propane, with manifold pressures of 4.0 in WC (natural gas) and 9.0 in WC (propane).
Highlights
Models
One canonical page per model with input, output and efficiency kept separate.
Laars Heating Systems
The Laars JX050 is the smallest Mini-Therm JX boiler: a non-condensing gas-fired residential hydronic boiler at the 50 size step of the 50-200 MBTU/h range, with LED-based analog diagnostics and no digital display.
Laars Heating Systems
The Laars JX075 is the second Mini-Therm JX size: a non-condensing gas-fired residential hydronic boiler at the 75 step of the 50-200 MBTU/h range, with LED-based analog diagnostics and no digital display.
Laars Heating Systems
The Laars JX100 is the mid-range Mini-Therm JX boiler: a non-condensing gas-fired residential hydronic boiler at the 100 size step of the 50-200 MBTU/h range, with LED-based analog diagnostics and no digital display.
Laars Heating Systems
The Laars JX125 is the upper-mid Mini-Therm JX boiler: a non-condensing gas-fired residential hydronic boiler at the 125 size step of the 50-200 MBTU/h range, with LED-based analog diagnostics and no digital display.
Laars Heating Systems
The Laars JX150 is the second-largest Mini-Therm JX boiler: a non-condensing gas-fired residential hydronic boiler at the 150 size step of the 50-200 MBTU/h range, with LED-based analog diagnostics and no digital display.
Laars Heating Systems
The Laars JX200 is the largest Mini-Therm JX boiler: a non-condensing gas-fired residential hydronic boiler at the 200 size top of the 50-200 MBTU/h range, with LED-based analog diagnostics and no digital display.
| Specification | Laars JX050 | Laars JX075 | Laars JX100 | Laars JX125 | Laars JX150 | Laars JX200 |
|---|---|---|---|---|---|---|
| input-min | — | — | — | — | — | — |
| Maximum input (as printed) | 50 MBH | 75 MBH | 100 MBH | 125 MBH | 150 MBH | 200 MBH |
| output-max | — | — | — | — | — | — |
| afue | — | — | — | — | — | — |
| turndown | — | — | — | — | — | — |
| vent-max-3 | — | — | — | — | — | — |
| vent-max-2 | — | — | — | — | — | — |
| weight | — | — | — | — | — | — |
Read the full comparison: Laars JX050 vs JX075 →
Read the full comparison: Laars JX075 vs JX100 →
Read the full comparison: Laars JX100 vs JX125 →
Error codes and alerts
No alerts documented for this series yet.
Manuals
Where ROMA provides on-site service
On-site service is currently offered in Greater Vancouver, BC, including Vancouver, Burnaby, Richmond, Surrey, Coquitlam, North Vancouver, West Vancouver, New Westminster, Port Coquitlam, Port Moody, Delta, Langley, Maple Ridge, Abbotsford, Chilliwack, White Rock, Pitt Meadows, Tsawwassen, Anmore, Lions Bay, Belcarra, Bowen Island, Mission. Everything else on this site is reference information you can use anywhere in Canada.
Services for Laars Heating Systems boilers
No. The JX has no digital display and no numeric codes: its installation manual (Document 1478C) diagnoses faults through the control's LEDs and the troubleshooting table and flow charts in Section 11.C and 11.D.
The manual covers sizes 50-200 MBTU/h and its parts lists carry six sizes: 50, 75, 100, 125, 150 and 200 (the JX050 through JX200 model steps).
Yes. The manual's parts sections list propane orifices, pilot parts and regulator springs, with altitude groupings printed for propane to 10,000 ft. Fuel setup is a licensed gas-fitting task done with the rating plate and conversion parts.
Describe what the boiler is doing and get a straight answer about the next step.
On-site service in Greater Vancouver, BC. ROMA lists “Open 7 days” on its site; call to confirm same-day availability.
Sources and verification
Facts checked September 7, 2026. Last updated September 7, 2026. Technical reviewer: not yet assigned.