Can anyone please help diagnose an intermittent fault on a Potterton Netaheat 10/16 Electronic Boiler?
The CH system was installed about 20 years ago and in use since. It is a fully pumped system, with thermostatically controlled radiators, a seven day programmer controlling motorised valves to separate CH and HW tank circuits. The boiler is wall mounted in the ground floor kitchen, the Groundfoss Pump and HW tank are located in the first floor airing cupboard and the CH system has an open header tank with a ball valve mounted on a platform in the loft. A heated towel rail in the first floor bathroom provides the principle circulation route should all the individual radiator thermo-valves happen to be closed. The system seems balanced with hot water reaching all radiators. The motorised valves failed and were replaced a couple of months ago - the system being drained down for this purpose.
Most of the CH system components are original. The exceptions are the boiler air pressure switch, which failed and was replaced just a couple of years after the original installation and the pilot Spark Earthing Bracket which was heavily eroded away and replaced one year ago. The pilot electrode and lead was also replaced at that time.
Most of the time, the boiler appears to start up as normal (fan, casing pressurised, pilot valve, spark ignition, main gas valve, burner ignition) and stop when the water being pumped through the heat exchanger reaches the temperature set on the thermostat.
There are two separate (but probably related) problems:-
1. bursts of rapid loud clicking, which I believe to be rapid operation of the Gas Control Valve. The main burner flame may flicker slightly during these episodes, but it I cannot be certain as it is difficult to see this through the small viewing port. It certainly remains alight (but that may be due to the speed of the on/off valve action).
These bursts of rapid clicks appear to vary in length from just two or three in a cycle to a large number (too many to count) over periods up to 10 seconds. Several bursts can occur during an on/off water heating cycle, but always fairly closely spaced together. The frequency and duration of the event seems random. Sometimes it does not occur at all for several days. On other occasions it has become so frequent the boiler has been turned off in fear that some damage may occur.
2. the boiler commences to light up as normal, but stops with the pilot light lit. That is, there is no click from the solenoid valve and the main burner does not light at all. The lit pilot light is clearly visible through the viewing port. No spark in then evident. This is a much more infrequent event. It seems to put itself right after having been left for a while. It does not seem to matter whether the boiler is hot or cold for this to occur.
Now having only just found this site and read some of the posts, this next bit will no doubt cause a big response. I have dismantled the boiler as per the original Potteton servicing instructions (there are just three screws for the controls, four for the outer casing and four for the chamber front panel), except I have not , nor ever will touch the gase components, such as the Gas Control Valve or the main burner. However, there is no point in denying that I have been inside, it has happened
.
In fact I am a bit confused by this as I thought the whole point of a fan presurised casing and dual flue was to provide a safe system. The fan draws fresh air in from the outside, that pressurises the outer case, feeds oxygen to the inner burner chamber (from below) and pushes the exhaust gases out through the flue. The pressure switch ensures that there is indeed a positive pressure before allowing the burner to operate. If there is a slight leak between the outer casing and its seal, that would allow air drawn in from the fan to escape into the room. A big leak would be detected by the pressure switch. How can exhaust gasses escape from the inner combustion chamber into the outer casing, which is at a higher pressure and then into the room?
Anyway, the insides were all fairly clean and all insulation, wires and equipment appear to be OK from a visual inspection. The spark earthing bracket, electrode and lead all look in their fairly new condition.
Altering the boiler water temperature thermostat also does not seem to affect the problem.
I cannot diagnose whether the problem is in the gas control valve itself, the electronic control box, or the flame detection system.
I would very much appreciate some advice.
The CH system was installed about 20 years ago and in use since. It is a fully pumped system, with thermostatically controlled radiators, a seven day programmer controlling motorised valves to separate CH and HW tank circuits. The boiler is wall mounted in the ground floor kitchen, the Groundfoss Pump and HW tank are located in the first floor airing cupboard and the CH system has an open header tank with a ball valve mounted on a platform in the loft. A heated towel rail in the first floor bathroom provides the principle circulation route should all the individual radiator thermo-valves happen to be closed. The system seems balanced with hot water reaching all radiators. The motorised valves failed and were replaced a couple of months ago - the system being drained down for this purpose.
Most of the CH system components are original. The exceptions are the boiler air pressure switch, which failed and was replaced just a couple of years after the original installation and the pilot Spark Earthing Bracket which was heavily eroded away and replaced one year ago. The pilot electrode and lead was also replaced at that time.
Most of the time, the boiler appears to start up as normal (fan, casing pressurised, pilot valve, spark ignition, main gas valve, burner ignition) and stop when the water being pumped through the heat exchanger reaches the temperature set on the thermostat.
There are two separate (but probably related) problems:-
1. bursts of rapid loud clicking, which I believe to be rapid operation of the Gas Control Valve. The main burner flame may flicker slightly during these episodes, but it I cannot be certain as it is difficult to see this through the small viewing port. It certainly remains alight (but that may be due to the speed of the on/off valve action).
These bursts of rapid clicks appear to vary in length from just two or three in a cycle to a large number (too many to count) over periods up to 10 seconds. Several bursts can occur during an on/off water heating cycle, but always fairly closely spaced together. The frequency and duration of the event seems random. Sometimes it does not occur at all for several days. On other occasions it has become so frequent the boiler has been turned off in fear that some damage may occur.
2. the boiler commences to light up as normal, but stops with the pilot light lit. That is, there is no click from the solenoid valve and the main burner does not light at all. The lit pilot light is clearly visible through the viewing port. No spark in then evident. This is a much more infrequent event. It seems to put itself right after having been left for a while. It does not seem to matter whether the boiler is hot or cold for this to occur.
Now having only just found this site and read some of the posts, this next bit will no doubt cause a big response. I have dismantled the boiler as per the original Potteton servicing instructions (there are just three screws for the controls, four for the outer casing and four for the chamber front panel), except I have not , nor ever will touch the gase components, such as the Gas Control Valve or the main burner. However, there is no point in denying that I have been inside, it has happened
.In fact I am a bit confused by this as I thought the whole point of a fan presurised casing and dual flue was to provide a safe system. The fan draws fresh air in from the outside, that pressurises the outer case, feeds oxygen to the inner burner chamber (from below) and pushes the exhaust gases out through the flue. The pressure switch ensures that there is indeed a positive pressure before allowing the burner to operate. If there is a slight leak between the outer casing and its seal, that would allow air drawn in from the fan to escape into the room. A big leak would be detected by the pressure switch. How can exhaust gasses escape from the inner combustion chamber into the outer casing, which is at a higher pressure and then into the room?
Anyway, the insides were all fairly clean and all insulation, wires and equipment appear to be OK from a visual inspection. The spark earthing bracket, electrode and lead all look in their fairly new condition.
Altering the boiler water temperature thermostat also does not seem to affect the problem.
I cannot diagnose whether the problem is in the gas control valve itself, the electronic control box, or the flame detection system.
I would very much appreciate some advice.
