The Baxi 625 Heat Only Boiler is a 25kW wall-mounted gas condensing conventional boiler from the highly regarded Baxi 600 series. Carrying a 7-year parts and labour warranty and achieving ErP class A space heating efficiency at 93%, it is designed for larger homes with high central heating demands. Suitable for both fully-pumped open-vent and sealed systems, and requiring no pump overrun or permanent live, it is one of the most installer-friendly conventional boilers on the market.
7-Year
Parts & labour warranty
17.4 kg
Installer lift weight
ErP A
Space heating class
⚠ Installer notice: Installation must be carried out by a Gas Safe registered engineer in line with current Gas Safety (Installation & Use) Regulations. The Benchmark Commissioning Checklist must be completed and handed to the user upon commissioning.
ℹ System flexibility: The Baxi 625 is compatible with both open-vent and sealed heating systems, making it a versatile choice for both replacement and new-build projects. No permanent live is required, simplifying the wiring process on site.
Key Features
25 kW Output — Ideal for Larger Homes
With a maximum output of 25kW and a minimum of 7.5kW, the 625 is well-suited to larger properties with 15+ radiators. Proportional modulation prevents short-cycling and maintains consistent room temperatures.
93% ErP Efficiency — Class A Rated
Achieving 93% Boiler Plus ErP efficiency and SEDBUK 89.1%, the 625 qualifies as an ErP Class A space heating appliance. Condensing operation extracts additional heat from flue gases to maximise fuel economy.
7-Year Parts & Labour Warranty
Registered through Baxi after installation by a Gas Safe engineer, the 625 is covered by a full 7-year parts and labour warranty — protecting homeowners and reducing installer liability.
No Pump Overrun & No Permanent Live
The Baxi 625 requires no pump overrun and no permanent live supply. Installation is simpler and faster compared to boilers that need additional wiring, reducing both time on site and disruption to the household.
17.4 kg Installer Lift Weight
At only 17.4 kg, the 625 is straightforward to single-hand lift onto the wall bracket — despite delivering 25kW of output. Its 370 × 625 × 270mm footprint allows cupboard siting with just 5mm side clearance.
Quick & Easy Servicing
Front and side access panels allow full servicing access without special tools. The easy-fit wall bracket features a positive fix with an audible locking click to confirm secure installation.
Flexible Concentric Flue System
The included telescopic 60/100mm concentric flue (315–500mm) suits the majority of installations. Top or optional in-case rear flue exit is supported, with a maximum equivalent run of 6 metres.
OpenTherm Ready & Hydrogen Blend Certified
Compatible with Certified OpenTherm controls for weather-compensating modulation and Boiler Plus compliance. The 625 is also certified to run on an 80/20 natural gas/hydrogen blend.
Technical Specification
| MPN / Product Code |
7712022 |
| Model |
Baxi 625 Heat Only |
| Series |
Baxi 600 Heat |
| Heat output (max) |
25 kW |
| Heat output (min) |
7.5 kW |
| Heat input – max gross (QnHs) |
28.62 kW |
| Heat input – min gross (QnHs) |
8.59 kW |
| ErP space heating efficiency |
93% (Class A) |
| SEDBUK 2009 efficiency |
89.1% |
| NOx class / NOx |
Class 6 / 24 mg/kWh |
| Sound power level (LWA) |
45 dB(A) indoors |
| Gas supply connection |
22mm |
| Inlet supply pressure (natural gas) |
20 mbar |
| Maximum gas rate |
2.73 m³/hr |
| Electrical supply |
230V / 50Hz |
| Power consumption |
33 W |
| Permanent live required |
No |
| Pump overrun required |
No |
| External fuse rating |
3A |
| IP rating |
IPX4D |
| Flue type |
60/100mm concentric |
| Standard flue length |
315–500mm telescopic |
| Max equivalent flue length |
6 m |
| Flow / return pipe size |
22mm |
| Condensate pipe size |
21.5mm |
| Compartment ventilation required |
No |
| Boiler width × height × depth |
370 × 625 × 270 mm |
| Installer lift weight |
17.4 kg |
| Gross packaged weight |
19.5 kg |
| System compatibility |
Fully-pumped open-vent or sealed |
| Warranty |
7-year parts & labour |
Frequently Asked Questions
What size home is the Baxi 625 suitable for?
The 625's 25kW output suits larger homes, typically with 15 or more radiators, or properties with high heat-loss. Paired with a well-sized indirect cylinder, it provides reliable central heating for multi-bathroom family homes.
Does the Baxi 625 require a pump overrun circuit?
No. The Baxi 625 is engineered to operate without a pump overrun or permanent live. Only a switched live is needed. This reduces wiring complexity and makes it a fast, straightforward replacement for older conventional boilers.
Can it be fitted inside a kitchen cupboard?
Yes. With a 5mm minimum side clearance and a depth of 270mm, the 625 fits inside a standard kitchen cupboard with ease. The optional in-case rear flue helps achieve a neat concealed installation. No compartment ventilation is needed.
Is the Baxi 625 compatible with OpenTherm controls?
Yes. The boiler supports Certified OpenTherm technology, enabling it to be paired with controls such as the Baxi uSense 2. This allows proportional modulation based on outdoor conditions, reducing seasonal energy consumption.
What warranty is included?
The Baxi 625 comes with a 7-year parts and labour warranty when installed and registered by a Gas Safe engineer. Benchmark Commissioning documentation must be completed to maintain warranty validity.
Is the Baxi 625 hydrogen blend compatible?
Yes. Baxi has certified the 625 for use with an 80/20 natural gas/hydrogen blend, meaning the boiler is ready for the planned transition to lower-carbon gas supplies without requiring modification.
