The Netaheat Electronic was the next major development in the design of this pathleading boiler. All the control logic, which had previously been shared between a collection of mechanical, electrical and electronic parts was combined into one integrated electronic control board. Flame supervision which had previously been carried out mechanically by the mercury vapour sensor became electronic, using flame rectification in the control board. The spark ignition was provided by the control board now, as was monitoring the fan as was controlling the gas flow to the pilot and main burners by switching on and off the two gas valve solenoids.
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 crucially important to replace the case correctly and prove this has been done by carrying out the case seal checks 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 long obsolete and for a while Potterton used to sell an upgrade kit containing a generic Honeywell air pressure switch. I'm now told this is no longer available either but I have yet to check. I see no technical reason not to fit a generic air pressure switch of the same specification. The air pressure switch often turns out to actually be in perfectly good working order, and the fault is a blocked air restrictor. Cleaning or replacing the air restrictor usually makes the air pressure switch (and the boiler) work after all! I suspect an awful lot of Netaheats have been scrapped unnecessarily due to this fault as few technicians realise the restrictor exists and is prone to blocking. Occasionally I find a different the reason for the air pressure switch not switching. Inside the boiler there are two aluminium tubes running from the fan at the top, down to the bottom of the boiler, to transmit the air pressure difference from the fan to the air pressure switch in the base of the boiler. These pipes suffer from corrosion and sometimes they corrode right through (particularly behind the fixing clips), preventing the air pressure switch from correctly sensing fan pressure. New tubes can be fitted to rectify this.
3) Control board failure.
Having so many functions, the control board can fail in a variety of different ways. The burners may randomly light and go out, or simply refuse to light. The Pilot may light but the boiler fails to progress to main burner ignition, sometimes with the pilot ignition spark continuing indefinitely. The boiler may also seem to start it's ignition sequence correctly by running the fan, but then shut down and start over again repeatedly and rarely progress to lighting the pilot. Sometimes the pilot flame lights but the main burners don't unless the boiler is given a whack, which is usually caused by some dry joints on the control board which can often be identified and re-soldered. Other times it's a jamming relay which means a new control board.
4) Combined Gas Valve failure
The combined gas valve turns the gas on and off to the pilot light and to the main burner in response to electrical signals from the other controls, and it regulates the gas pressure to the main burner. Either of the solenoids which turn the gas on and off may fail and will be necessary to fit a new combined gas valve. Unfortunately the gas valve is no longer available and the only source is eBay. There are usually three or four second-hand ones for sale at any given time, along with the occasional new one. Accurate diagnosis is the key here though, as there is a control board fault which looks for all the world like gas valve failure to an inexperienced technician. Many Netaheats have been scrapped with suspected gas valve failure when the fault actually lies in a soldered joint on the control board which fails from heat stress. Re-soldering the joint (or replacing the whole board) will bring the boiler back to life.
5) Pilot light failing to light.
This is a common problem with a variety of causes. Sometimes there is no spark, which is usually caused by the air pressure switch failing to detect the fan running. A new air pressure switch or sometimes simply cleaning debris from the restrictor in the air pressure switch usually fixes this, but sometimes the control board has failed and simply isn’t delivering a spark. A new control board will be needed. If there IS a spark but no pilot flame, the gas control valve may have failed to open or the ignition earth electrode may be heavily eroded, leading to a spark in not quite the right place to ignite the gas. See the photo below of a badly eroded earth electrode (on the right) alongside a new one (on the left). Notice the horizontal section is completely missing from the old electrode on the right. This will easily prevent the boiler from lighting.
6) Pilot alight but main burner failing to light.
Two possibilities here. If the spark is continuing even though the pilot flame is alight, the control board is failing to detect the pilot flame, and is continuing to try to light it even though it is already alight. If/when it detects the flame, it will light the main burner. The control board may be faulty or it may be caused by an eroded earth electrode, as shown in the photo above. If the sparking stops the instant the pilot flame ignites, the control board has detected the flame and should be opening the gas valve main burner solenoid. If there is 240Vac on the main burner solenoid terminals then this is gas valve failure, if there is no voltage then it is control board failure.
7) 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.
8) 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 Electronic is an easy boiler to diagnose and repair. It became the template for virtually all other wall-hung gas designed in the 1990s. The fanned flue, the combined gas valve, the integrated electronic control board using the air pressure switch and flame rectification for combustion supervision were all features copied by virtually every gas boiler manufacturer across the world. The only thing remaining wrong with the Netaheat was the positive case pressure design, which had lead to a number of deaths following incorrect re-fitting of the case after servicing or repair. This was corrected in the next incarnation of the Netaheat, the Netaheat Profile.
If you'd like me to fix your Netaheat, contact me here.
First published 2nd January 2011
Last updated 15th October 2018