Bosch Thermotechnology · Greenstar Combi (100p/151p)
Bosch Greenstar Combi 151p (ZWB 42-3A)
The Greenstar Combi 151p is the ZWB 42-3A wall-hung combi — the largest Greenstar combi: 36,000 to 151,600 BTU/hr heating input, DHW output to 135,800 BTU/hr at a 140 °F outlet and 3.61 GPM nominal DHW flow, covered by the Combi 100P/151P I&O manual.
Key figures
- Max input
- 151.6 MBH
- Max CSA output
- 137.5 MBH
- AFUE
- —
- Min input
- 36 MBH
Input is gas energy consumed; output is heat delivered. Never size from input alone.
Bosch Greenstar Combi 151p (ZWB 42-3A) in practice
The combi 151 p, engineering code ZWB 42-3A, is the biggest wall-hung combi in Bosch's current Canadian Greenstar line: 36,000 to 151,600 BTU/hr natural-gas heating input at sea level with the altitude tables stepping down through 7,000 ft. Its built-in DHW module outputs up to 137,500 BTU/hr at a 113 °F outlet and 135,800 BTU/hr at 140 °F.
The domestic side is where the 151 p separates from the 100 p: a maximum DHW flow rate of 3.963 GPM and 3.61 GPM nominal at a 140 °F outlet, versus 2.64/2.03 GPM on the ZWB 28-3A. DHW pressure is approved to 150 psi, the expansion vessel holds 3.17 gal and the whole appliance weighs 110.2 lb in the shared 440 x 850 x 353 mm wall cabinet.
The Combi 100P/151P manual (6721853953, 11.2025) documents the 151 p's Table 33 fault codes and vent tables; the same unit also appears in the Greenstar Wall I&O, whose vent tables for the 35/42 class give different maximum 2" concentric lengths — Boilers.ca's model pages cite both manuals so a code or a vent run can be checked against the correct table.
Best suited to
- Larger homes whose heat loss and simultaneous hot-water draws justify the 42-class combi
- Households wanting 3.61 GPM nominal DHW flow without a separate tank
- Wall-hung combi replacements at the top of Bosch's Greenstar wall range
Applicability and support
- Model number
- ZWB 42-3A
- Canadian availability
- available
- Production status
- current
- ROMA supplies
- Confirmed at consultation
- ROMA services
- Confirmed at consultation
- Warranty
- Not verified
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.
Specifications
Published specifications
Values as published by Bosch Thermotechnology. Units are shown with every value; notes flag conflicting sources or missing figures.
| Specification | Value | Note |
|---|---|---|
| Input | ||
| Input rate, minimum | 36 MBH | 36,000 BTU/hr at 180/79 °F (82/26 °C), natural gas. |
| Input rate, maximum | 151.6 MBH | 151,600 BTU/hr at 180/79 °F (82/26 °C), natural gas; altitude tables in the manual reduce the maximum above 2,000 ft. |
| Output | ||
| Output rate, maximum (104/86 °F) | 137.5 MBH | 137,500 BTU/hr at 104/86 °F water temperatures per the manual technical table. |
| Domestic hot water | ||
| DHW output rate (113 °F (45 °C) outlet) | 137.5 MBH | 137,500 BTU/hr per the manual technical table. |
| DHW output rate (140 °F (60 °C) outlet) | 135.8 MBH | 135,800 BTU/hr per the manual technical table. |
| Maximum DHW flow rate | 3.963 gpm | Maximum domestic hot water flow rate per the manual technical table. |
| Nominal DHW flow rate (140 °F outlet) | 3.61 gpm | Nominal domestic hot water flow at a 140 °F (60 °C) outlet temperature. |
| Maximum approved DHW pressure | 150 psi | 150 psi (10.3 bar); minimum water pressure 4.35 psi (0.3 bar). |
| Venting and air | ||
| Venting | 2" NG only; 3" or 3"/5" (80/125 mm) concentric for LPG | Per the manual: the 35/42 model class is limited to 25 ft of straight 2" concentric pipe with 2 elbows (NG), or 44 ft of 3"/5" concentric pipe with 1 elbow. Termination type changes the tables. |
| Physical and connections | ||
| Weight (without packaging) | 110.2 lb | 110.2 lb without packaging per the combi-100p/151p manual (kg figure printed 48 in the 42-3A table and 50 in the 28-3A table). |
| Dimensions (W x H x D) | 17-21/64" × 33-15/32" × 13-57/64" (440 × 850 × 353 mm) | Per the manual technical data table. |
| Sound pressure level | ≤ 45 dB(A) | Per the manual technical data table. |
| Maximum supply temperature | 187 °F | 187 °F (86 °C). |
| Maximum permissible operating pressure (PMS), heating | 30 psi | 30 psi (2.07 bar). |
| Expansion vessel total contents | 3.17 gal | 3.17 gal (12 l); pre-charge pressure 10.9 psi (0.75 bar). |
| Permissible inlet gas pressure | NG 3.5–10.5 in. W.C.; LPG 8–13 in. W.C. | NG is the factory default; LPG only after successful gas conversion with the included conversion kit. |
| Operating limits and other | ||
| Fuel | Natural gas or propane | Separate NG and LPG ratings in the manual; LPG requires the gas conversion kit included with the appliance. |
Manuals
Frequently asked questions
What does 151p mean next to the code ZWB 42-3A?
The 151p is the Bosch CA manual-title name for the ZWB 42-3A combi (the 100p name covers the ZWB 28-3A). The model record follows the engineering code, which is what appears on the rating plate and in the technical tables.
How does the 151p compare with the 100p on hot water?
The combi manual prints 3.963 GPM maximum and 3.61 GPM nominal DHW flow at a 140 °F outlet for the 151 p, against 2.64 and 2.03 GPM for the 100 p. DHW output at 140 °F is 135,800 BTU/hr versus 91,400 BTU/hr.
Which vent class is the ZWB 42-3A in?
The 35/42 class: 25 ft of straight 2" concentric pipe with two elbows (NG) per the Wall manual's tables, or the model columns of the combi manual for concentric installations — so the vent route must be checked against the tables before installation.
Questions about the Bosch Greenstar Combi 151p (ZWB 42-3A)?
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
- Bosch Home Comfort Canada — Greenstar Boilers · accessed September 7, 2026
- Greenstar Combi 100P and 151P Installation and Service Manual (6721853953) · accessed September 7, 2026
- Greenstar Wall Boilers Installation and Service Manual (6721853955) · accessed September 7, 2026
Facts checked September 7, 2026. Last updated September 7, 2026. Technical reviewer: not yet assigned.