Portrait photo of Mike Bryant, AKA Mike the Boilerman

Mike the Boilerman -

Your Gas Safe Registered boiler 

and central heating repair technician in west Berkshire. Willing to travel :)



I am still carrying out house visits. Full details explained


(Last updated 21st April 2021)

Potterton Kingfisher, Kingfisher 2 and Kingfisher MF gas boilers:

If your Potterton Kingfisher has failed, it can usually still be fixed despite its age, even the very oldest versions. The early Kingfishers and Kingfisher Twos are really simple, basic and reliable boilers originally designed in the 1980s with very little to go wrong. If yours won’t light, you’re very unlucky! The later version Kingfisher MF is more complex and works in a completely different way, but breakdowns are generally still fixable. If you’d like me to visit to fix your Potterton Kingfisher, get in touch. Call or text me on 07866 766364.

What to check if your Potterton Kingfisher (not MF) stops working:

1) The pilot light. This is the No 1 fault on these. Pull the front off the boiler and look inside to see if the pilot flame is present. If no flame, this will be why it doesn’t work and it needs lighting. There are instructions on the back of the front panel you just removed. I’ll record a video of how to light one next time I work on a Kingfisher, but in the meantime here is a helpful video posted on YouTube by a chap called Christopher Mahon.

2) Check the heating is set to ON at the programmer or time switch.

3) Check the room thermostat is at a ‘high’ setting.

4) Check this white temperature control knob in the boiler is set to a high setting, and not set to OFF. In this screenshot from the video it is set to ‘4’.

5) If your pilot flame was out and you successfully re-lit it, check you remembered to turn the the black control knob the final quarter turn to the ‘flame’ position. This is easy to forget, I know this from experience :) The black control knob  can be clearly seen in the video, set to the ‘flame’ position. 

If you’ve done all the above with no joy, or if the pilot flame keeps going out, you’ll need a visit from a boiler technician. Call me if you wish on 07866 766364. I’m based in Great Bedwyn, near Hungerford, Berkshire, and am happy to travel. You can also text me on that number. 

Potterton Kingfisher description and history:

The Potterton Kingfisher boiler started life as a simple and basic floor standing boiler. Despite most boilers being wall-hung by the 1980s/1990s there was still a rump of demand for an old style boiler standing on the floor to connect into a vertical chimney, or have that newfangled type of flue which passes horizontally to outside through the wall. 

The Kingfisher 2 was the next model launched, but was just a facelift version and is broadly identical inside and technically. Both very basic boilers. A cast iron heat exchanger is heated by a gas burner in the base of the boiler. The gas is lit by a permanent pilot light, and turned on and off to control the boiler temperature by a thermostat with a sensor inside the heat exchanger. The ‘multi-function gas valve’ supervises the pilot flame using a thermocouple, turns the gas on and off to the main burner, and regulates the gas pressure to the burner. The gas pressure is adjustable to allow the heat output of the boiler to be set to suit the heat load connected to the boiler. A really basic, ultra-reliable and easy-to-maintain boiler. Cherish yours if you have one!

When regulations preventing installation of permanent pilot light boilers came along, Potterton launched the “Kingfisher MF” in response for the same market. Still a floor standing boiler but now totally different inside, with electronic ignition and fan-powered flue, and a printed circuit board to control everything and provide flame monitoring. FAR less reliable and a major step backwards in my personal opinion, but there we are, the politicians insist we now use these marginally-more-fuel-efficient-but-hugely-more-complex boilers now. This suits me fine as mending them has turned into a career for me!

So we have two completely different boilers both called Kingfisher, and each has it’s own set of faults and common breakdowns. As follows:

Kingfisher and Kingfisher 2:

Thermocouple failure. 

This is the weakness in all ‘Old Skool’ boilers with a permanent pilot light. The thermocouple is the safety device that turns the gas OFF if the flame goes out. The Thermocouple tip is heated by the pilot flame, the heat creates an electric current which operates an electro-magnetic valve which keeps the gas ON. If the pilot flame goes out for any reason, the thermocouple cools, the electrical current stops and the thermo-electric valve springs closed, shutting off the gas. This also happens when the thermocouple fails, and the user is unable to make the pilot flame stay alight as there is no electrical current. A new thermocouple is needed, which is quick and easy to fit. A similar effect can occur due to lack of regular servicing, where the pilot flame size or shape is affected by dust, debris etc which would be removed during servicing. The reduced or changed pilot flame shape no longer properly envelopes and heats the thermocouple tip.

Gas valve failure:

The thermoelectric valve in the gas valve is prone to failure resulting in identical symptoms to thermocouple failure above. A new gas valve is required. There are two types fitted to Kingfishers. One type is still available new and the other discontinued. If yours is the discontinued type there is a thriving market in second hand gas control valves so not all is lost, but if you or your gas technician is unhappy with a used component, the only option is to replace the boiler.

Thermostat failure:

The temperature control knob is attached to the variable temperature thermostat spindle. This thermostat senses the temperature inside the heat exchanger and occasionally loses its calibration. A new thermostat is probably still available. Quite a rare failure though, and I haven’t needed to replace a thermostat on a Kingfisher for many years.


This is where the boiler pops and bangs as it heats up, making a noise like an electric kettle approaching boiling. The usual cause is corrosion contamination inside the heat exchanger. Not an important problem and many users elect to just live with it and ignore it. The corrosion can sometimes be removed by power flushing, or ‘boiler quietening’ chemicals can be added to the circulating water. Results are variable and no guarantees of a fix for ketling can be given. 

These are bout the only problems a basic Kingfisher suffers from. If you have one, I suggest you keep it!


Kingfisher MF:

The Kingfisher MF is a totally different boiler inside, despite being a floor standing boiler looking broadly like the older Kingfisher. The MF is significantly more fuel-efficient due to having fully automatic electronic ignition, no permanent pilot light, electronic flame detection and a fan-powered flue (even the open flue versions with a vertical chimney) all operated by a central electronic control board. Being a non-condensing boiler however, the Kingfisher MF was discontinued when condensing boilers became mandatory in 2005.


This boiler suffers from all the same failures as most fan flued non-condensing boilers. Fan failure, air pressure switch failure, PCB failure, gas valve failure etc.

The Kingfisher MF has overheat protection so should the heat exchanger overheat, the boiler ‘locks out’. ‘Locking out’ means the boiler illuminates a red ‘lockout light’ and turns itself off, requiring the user to reset boiler by pressing the ‘Reset’ button once the boiler had cooled for a while. The ‘Lockout’ light would be better labeled “overheat” in my personal opinion, as this is what it actually means.  

There are three common causes of overheating in the heat exchanger, leading to locking out:

1) An external fault, nothing to do with the boiler. No bypass circuit fitted by the installer. The boiler runs the pump for a few minutes to distribute residual heat after the burners shut down, and if the heating system installer does not ensure there is a water circuit available for this water flow after shut-down, the residual heat will not be distributed and the boiler will occasionally (or regularly) lock out. 

2) The pump over-run function on the boiler failing, so residual heat in the heat exchanger after boiler shut-down no longer gets distributed.

3) Dirty system water. Corrosion deposits getting picked up from inside radiators etc and being carried into the heat exchanger and deposited there, where they stay for ever and prevent heat in the cast iron passing through into the water.

There is one further possible reason for locking out…

On the vertical flue (open flue) versions, fresh air is drawn from the room into the top of the boiler to dilute and cool the hot flue gasses rising up the chimney. Should the chimney flue get blocked, those potentially dangerous hot flue gasses can spill out through the air intake into the room containing the boiler as they can no longer pass up the chimney flue. To guard against this spillage there is a spillage thermostat (often referred to as a “TTB sensor”) mounted in the air intake which trips when spillage occurs, also putting the boiler into ‘Lockout’. So if your Kingfisher is the vertical chimney flue version and locking out, it is possible there is a fault with the flue rather than it overheating.

Common faults and fixes:

1) Pilot flame failure. This boiler has a pilot light which only runs when the boiler is ON. It shuts down when there is no demand for heat. When there is demand for heat, the pilot flame lights first then about one second later the pilot lights the main burner. This misleads owners and technicians into not realising there is a separate pilot light at all. I’d go as far as to say most Kingfisher MF failures revolve around the pilot failing to light and the possible reasons for this deserve a sub-section all of their own.

1a) If the pilot flame is failing to light, a common cause is a blocked pilot injector. The burner assembly and pilot assembly are at floor level and on open flue versions terribly prone to contamination with dirt and dust, although blockage can occur on both open and balanced flue versions. The injector can sometimes be cleared with a piece of 5A fuse wire but take care, it is made from soft aluminium. Better to replace with a brand new injector. 

1b) If the injector is not blocked then either there is no gas supply to the pilot or there is no spark. Or both. When neither gas nor spark are present this usually indicates flue fan failure or air pressure switch (APS) failure. (The APS detects the fan running before allowing gas and spark to the pilot.)

1c) If there is gas but no spark, either the PCB is failing to produce a spark or the ignition lead is broken.

1d) If there is a spark but no gas, check for continuity across the gas valve pilot solenoid. The value should be around 2,000 Ohms. If you get this correct value check for 175Vdc on the terminals (beware this high DC voltage is DANGEROUS). No voltage suggests PCB failure, DC voltage present suggests mechanical failure inside the gas valve. 

2) If there is a pilot flame present but no progression to ignition of the main burner, then the gas valve main burner solenoid is not opening. Apply the same checks to the main burner solenoid as to the pilot in 1d) above.  One perverse failure to mention is that on a boiler with PCB failure, the failure is sometimes caused by a gas valve fault. There is a ‘fusible resistor’ on the PCB that fuses when the gas valve fails meaning the gas valve failure looks to the engineer like a failed PCB. Just plugging in an expensive new PCB without replacing the gas valve solenoids for continuity first can result in the new PCB being damaged instead of the boiler starting to work. Beware!

If you would like me to repair your Potterton Kingfisher, contact me on my mobile 07866 766364

Post script:

Clearances and access:

All boilers require good front access for servicing and repair. Boilers fitted into the corners of kitchens and surrounded with kitchen units can be a particular problem in this respect. Access from the side makes a boiler far more difficult and time-consuming to work on, if it is possible at all.

The manuals for the earlier models of Kingfisher boiler state 61cm (two feet) of clear space is needed directly in front of the boiler, which in practice might be adequate, but only just. Three feet of space is far better. The manual for the MF models states 25cm (10 inches) which is quite impractical. I shall need an absolute minimum of two feet of clear floor space directly in front of any model of Kingfisher boiler to repair it, preferably three feet, and I will check this with you on the phone before accepting a booking to visit. (If I remember!)

Potterton Kingfisher temperature control knob, set to '4'.
Potterton Kingfisher MF boiler controls showing lockout light and reset button.

Diagram from the manual showing the MF boiler controls, including the lockout light and the reset button

Gas Safe Register Logo 2

Copyright Michael Bryant 2021

Site first published 16th January 2004

Last updated 26th April 2021

Gas Safe Register 197499, CIPHE registration number 56207

Chartered Institute of Plumbing and Heating Engineering logo 2

This website makes use of cookies. Please see my privacy policy for details.