Mike the Boilerman portratit photograph

Mike the Boilerman 

Your independent Potterton 

Netaheat specialist covering Berkshire, Wiltshire & surrounding counties

For more information or to book your breakdown repair, call or text me on 

07866 766364 

*Coronavirus* - Back at work now, policy here

The Netaheat Original by Potterton

The original Netaheat is not marked "Netaheat Original", but just plain "Netaheat". Understandable as at the time of launch they had no idea of how successful the new design would be so they were not necessarily expecting to launch further versions. Even the youngest of the Netaheat originals must be at least 30 years old now, and very rare. I remember installing them in my early days as a young and very green (not the environmental type of 'green') plumber! Very few parts are available for them now.

Here are the common problems:

1) Flue Fan Failure

As with most fanned-draught boilers, the most common failure on all versions of the Netaheat is failure of the fan. Combustion air is blown with an electric fan through the combustion chamber so it is a safety-critical component. If the fan fails to start, the safety device which tests to see if the fan is running before allowing the pilot to light will detect the failure and stop the boiler from lighting. To the user the boiler will stay silent (or possibly hum quietly) instead of bursting into life as normal when a demand for heat is turned on. The fan is still freely available as a spare part and is fairly straightforward to install, but as this boiler is a 'positive case pressure' boiler and replacement of the fan involves removing and replacing the case, it is important to carry out the case seal checks on reassembly as described in Gas Safe Register Technical Bulletin TB006, "Industry guidance for the checking of case seals and the general integrity of  room-sealed fan-assisted positive pressure gas appliances".

2) Air Pressure Switch failure

The safety device which tests the fan for correct operation is the air pressure switch. These are know to fail occasionally and the result is the fan runs, the boiler sounds for all the world as though it is about to light, but no ignition ever occurs. The correct air pressure switch is reported to be no longer available but there is no technical reason not to fit a generic air pressure switch of the same specification. Doing so may not be strictly in accordance with the Gas Regulations though. 

3) Mercury Vapour Valve Switch failure.

The micoswitch inside the mercury vapour valve switch tends to become unreliable with age. The boiler operates randomly, and if it refuses to light it will sometimes respond to a thump with a fist of the front! The switch itself cannot be replaced as it is inside the gas-way and needs to be of gas-tight design. The mercury vapour valve assembly has been obsolete and not available for many years now so failure of this component means replacing the whole boiler unless a second-hand mercury vapour valve switch can be sourced. They very occasionally appear on eBay. 

4) Solenoid gas valve failure.

The symptoms appear to be the same as air pressure switch failure above (i.e. the fan runs, the boiler seems about to light but never does). The difference is that the pilot light has lit, but the progression to lighting the main burner never happens. The solenoid gas valve became obsolete and unavailable in about 2002 and failure usually means replacing the whole boiler. I have never seen one for sale second hand or on eBay.

5) Spark generator failure.

The spark generator is a black box that delivers the spark to light the pilot light. They are no longer available but the design is simple and can often be repaired on site, usually by soldering in new capacitors. 

6) Pilot light failing to light or very small.

Easily fixed and associated with lack of proper servicing. A problem common on lots of boilers. The pilot jet has become blocked or partly obstructed with debris and needs poking out with some fusewire. Part of the manufacturer's service procedure!

7) Relay failure.

There is a generic, socket-mounted eight-pin relay in the control panel of this boiler. These occasionally fail causing the boiler to remain silent and inactive when there is a call for heat. This relay turns the combustion air fan on (amongst other functions) so when it fails, it looks much like fan failure. A new generic relay of the same specification is freely available from electronics suppliers..

8) Thermostat failure

The boiler overheats, basically. The water in the boiler reaches boiling point, a HUGE banging noise (described to me by more than one customer as sounding like someone trying to break into the house using a sledgehammer to smash through the wall) accompanied, if the customer notices, by a loft full of steam. The thermostat is still, as far as I know, freely available.

9) Cracks in combustion chamber insulation

This isn't really a fault at all, but I'm getting a steady trickle of customers calling or emailing to say their boiler has been condemned due to cracks in the heat insulation lining the combustion chamber. This is perfectly normal and most Netaheats have these hairline cracks, but unscrupulous technicians have been seizing on this as a spurious reason to class it as dangerous and try to sell the customer a new boiler. Netaheats are perfectly safe with these cracks, but if yours has them and you are still worried, I can make and fit new insulation panels from the correct ceramic fibreboard material.

The Netaheat original is bewildering to an engineer accustomed to modern boilers. It works in a TOTALLY different way. I have reverse-engineered the ignition sequence so if you are a Gas Safe Registered engineer needing to fault-diagnose a Netaheat original I can send you my Word document detailing the sequence to help you understand it. Email me and ask! 

If you'd like me to fix your Netaheat for you, contact me here or call or text my mobile, 07866 766364. 


By the way I’m based in Great Bedwyn, Wiltshire (near Hungerford) and these are the areas I cover: Berkshire, Gloucestershire, Hampshire, Oxfordshire, Surrey, Sussex, West London, Wiltshire.

Call or text me on 07866 766364



If your boiler has broken down contact me for free help and advice by phone or text. I can arrange to visit and repair if necessary.


 If you book a visit I shall wear a face covering (and gloves where practical), and observe social distancing.

Details here

Gas Safe Register logo

Copyright Michael Bryant 2021

Site first published 11th November 2010

Last updated 7th June 2021

Gas Safe Register 197499, CIPHE registration number 56207

Chartered Institute of Plumbing and Heating Engineering logo