Keston boilers
Keston is a boiler brand made by Ideal Boilers in Hull. Keston’s own manuals give Ideal’s address, and its spares come from the Ideal parts website. So if you know Ideal, Keston is a close cousin.
What makes Keston different is the twin flue. Most boilers have one flue that goes straight out through the wall. A Keston uses two thin pipes instead: one brings fresh air in, and one takes the fumes out. Keston says the flue on its newest combi and system boilers can run up to 27 metres. That means a Keston can sit well away from an outside wall.
The Keston range
Keston’s newest boilers end in 2. The Combi 2 comes in 30 kW and 35 kW sizes. The System 2 S30 is the system boiler, at 30 kW. The Heat 2 comes in 45 kW and 55 kW. Keston says it’s for large homes or light commercial use.
Older Keston boilers you may still find include the first Combi and System models, plus the C Series, K Series and Qudos. Keston still keeps the manuals for many of these on its website.
Words, not codes
A Keston Combi 2 doesn’t show a short code when something goes wrong. It shows a message in words, such as Low Water Pressure or Ignition Lockout. Under the message are simple steps, and a Restart button where a restart is allowed. Some messages just say Contact Installer. Those need a Gas Safe engineer.
The table on this page uses Keston’s own wording from the Combi 2 user guide. Older Keston boilers may work differently, so check the guide for your model.
Pressure
Keston’s guide asks you to fill the system to about 1.0 bar when it’s cold. When topping up, it says to stop at 1 to 1.5 bar. The boiler won’t work at all if the pressure falls below 0.3 bar. If the pressure keeps dropping, Keston says you should call a Gas Safe engineer. Our guide shows how to top up low boiler pressure.
Frozen condensate pipe
Keston explains what you’ll see when the condensate pipe freezes. First, the boiler gurgles and shows Blocked Flue/Condensate. If you restart it, it gurgles again and then shows Ignition Lockout.
The fix is to find the frozen part and warm it gently. Keston suggests a hot water bottle, a microwave heat pack or a warm damp cloth. You can also pour warm water over the pipe, but never boiling water. Keston also says not to thaw pipework above ground level. Leave that to an engineer. See our step-by-step guide on how to thaw a frozen condensate pipe.
Keston gas boiler ranges
These are the gas boiler ranges on the Keston website as of 21/10/2026.
- Combi 2 C30 and C35 Combi
- System 2 S30 System
- Heat 2 45 and 55
Older Keston ranges
You may still find these in homes. They are no longer sold new, but many are still working.
- Combi C30 and C35
- System S30
- C Series
- K Series
- Qudos
Common Keston fault codes
Codes can differ between models and ages of boiler. Always check the user manual for your exact model.
| Code | What it means | What you can do |
|---|---|---|
Low Water Pressure | The water pressure in the heating system is too low. | With the boiler off and the system cold, fill to 1.0 bar. Bleed the radiators, then top up to 1.0 bar again. |
Blocked Flue/Condensate | The condensate pipe or the flue may be blocked. In winter, this often means a frozen pipe. | Check the condensate pipe for ice or a blockage, and check the flue outside. If it stays, contact your installer. |
Ignition Lockout | The boiler failed to light after five tries. | Check your other gas appliances work. Restart the boiler once. If it stays, contact your installer. |
Overheat | The boiler got too hot. | Fill to 1.0 bar with the system cold, bleed the radiators and check the radiator valves are open. Then restart. |
Too Many Restarts | The boiler has been restarted too many times. | Contact your installer. |
Keston manuals
Keston puts its user guides and installation manuals on its own website. You can find Keston manuals here. You'll need your model name. The GC number helps too. Our guide shows you how to find your boiler's model and GC number.
Stay safe. You can reset a boiler, top up its pressure and thaw a frozen condensate pipe yourself. Anything inside the case is a job for a Gas Safe registered engineer.
If you smell gas, leave the building and call 0800 111 999.