HVAC Questions? Ask an HVAC Expert for Answers ASAP
I will be glad to help you if I can. Good morning.
Sorry, just noticed your message above. The boiler has been in about 7 years.
Yes, I am an Electronic engineer. Unfortunately, I cannot get to the boiler until 1730 GMT (now is 1305), but if you tell me what tests to do, I can do them later.
It seems more appropriate to describe the fault in an either or scenario. That is to say that either the 'w' wire that brings on the gas valve is shorting to ground or the controller is defective. Test continuity to ground on the conductor that carries the signal for heat from the thermostat and also incrementally test the same circuit to ground as it loops in series through each of the safety controls on the boiler.
Test the gas valve coil to ground as well. If you find continuity to ground on any large increment of control wiring tested, test smaller increments until the short is determined and remedy the situation.
If this makes sense to you, I can give you another method that might be easier for you that involves a box of 3 amp car fuses of a manually resettable 3 amp circuit breaker.
OK, I will try that. I hadn't appreciated that the heat signal from the thermostat loops through the thermistors on the pipes. (I will replace the thermistors tonight anyway).
Do you know of a site for a wiring diagram for the boiler at all?
not the thermistors, only through the safety switches like high limit and rollout. Thermistors read measurable resistance for the controller to convert to a numeric (temperature) value. Switches are either open or closed.
Let's not get into the cycle of replacing parts until we have verified the short. I am not a hit or miss advisor. I intend to guide you to the precise problem.
get back with me later
Thank you. Will do. Any possibility of finding a schematic?
Thank you. I will get back later. Up to what time are you around?
Checked the following:-
Gas valve body earthed.
Heat exchanger body earthed.
Ignition electrode plate earthed.
Connector removed from gas-valve
Gas-valve connections O/C to earth
(Gas valve resistance pin to pin 32 ohm)
Connector to gas-valve (when removed from gas-valve)
Blue 20K ohm to earth
Red 170K ohm to earth
"Demand" from heat thermostat is showing 230V (NB UK)
Hope this helps.
does o/c mean open no continuity? I would expect open to earth on the connectors as well. Some systems use the common side of the transformer to be grounded. but the power side should not have measurable resistance to ground. Here is the problem but we need to narrow it down. Isolate the path until it is narrowed down to a switch or a rub that has gotten through the insulation. I will look for a link to the schematic and get back with you. here is the link for the manual but there's no schematic http://www.vaillant.co.uk/stepone2/data/downloads/d7/42/00/ecoTEC_installation_and_servicing.pdf
I can't tell without a schematic which wire goes to the control load, but I noticed that it has a bus port for external data link for diagnostic tools. If you can't isolate the short you may have to call for service.
I would apply power directly to the gas valve so that we can eliminate that. Its all about eliminating variables at this point. You should be able to eliminate the damaged harness as well.
What voltage does the gas-valve use? It is unlikely to be 230V AC since the cableform is not that well insulated.
o/c is no continuity (open circuit)
Can you confirm that the gas-valve is 24V AC? I haven't measured the reistance in both directions (it didn't occur to me). If so, then I can do the test you described.
Just for info, after the fault first appeared, at some point pushing the reset button cleared the fault and the boiler worked for a while, but hasn't done so since. This is suggesting that something is "on the edge" of failure.
I've visually inspected the cableform to the gas-valve & it seems OK and it has been moved quite a bit, so any shorts to the case, pipes, or other conductors should have been cleared by now. I've also removed the printed circuit board and visually inspected it & can see some corrosion around the connector for the gas-valve. I've cleaned this & will refit later today (6pm GMT)
We can't see a schematic to know the voltage of the gas valve. V12 is right about the protocol for diagnosis being the same. One leg,( blue or red) should go to ground but the other leg needs to pass through the control and safety switches in series. Isolate the source of the short by removing wires incrementally (starting with the damaged harness that you found) and testing both wires and switches to ground until one reads continuity and bypass it temporarily and use the controller to see if the error code goes away. Be sure to remove the bypass and replace the safety switch upon completion.
Happy Thanksgiving to you sir and I will be back from time to time.
I will again opt out to allow V12 or others to contribute in my absence but rest assured that I have taken a personal interest in your situation.
I wonder if there are any Valiant techs in the UK who would be so kind as to weigh in on this issue. They would be of tremendous value to us at Justanswer because I know that they are a wonderful company who provide both manufacturing and service
Looking at the printed circuit board (PCB), I think that there is a circuit to measure the current to or from the gas-valve. I don't know if the wiring harness has a loop through condition on the PCB, but the loom itself is one to one at each end. This loom contains the thermistors, gas-valve, thermal fuse and air pump connections only. Other than the water pressure sensor, there are no further inputs. (Obviously there is the water pump and the spark generator also.)
Happy thanksgiving to you. (Iwasn't aware of the date of this holiday - we don't have it in th UK).
can you tell which leg of power to the gas valve goes straight to common and which leg has the loop through the other components (red or black)?
That is the leg that is causing the ground fault and thus the error code.
We need to isolate that path and each of the components in it's path until we find wher the continuity to ground is.
I think we can do this, it is on your schedule. I will come and go but the other guys can help you do this. We are almost finished and I have already had my hoiday and nap. If you are willing, we can proceed. You are doing great.
I've discovered the problem. A flexible water connecting tube (Vaillant part number XXXXXXXXXX had a small leak which has caused water to wick along the cableform to the circuit board (PCB). This (I think) had caused some of the connector pins on the PCB to show a lower than expected resistance between them. (The electronics seems to do measurements before it turns the gas-valve on). The amount of water was tiny, but over a period of 7 years, this had caused quite a noticable amount of deposits. Also, the boiler is installed in a garage which although not particularly damp is not heated, so the water did not have a chance to evaporate.
I cleaned off the deposits left by the water, refitted the PCB and it works.
Thank you all for your help and assistance.
Merry Christmas (when it gets here!)
Excellent deductive skills on your part. Technicians find this rare in engineers. I appreciate you and it was my pleasure in helping you'
Off the record I have an invention that I think might do well in the UK.
It is a retrofit for air conditioners so that they can be heat pumps.
Perfect for hybrid applications with boilers or any heating system that has an air conditioner that is not a heat pump from the factory.
I welcome your advice, as I esteem your opinion. It seems that Europeans in general have a more serious concern for global warming.
www.hybridupgrade.wordpress.com my contacts are available there.