How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask jj Your Own Question
jj, HVAC Mechanic
Category: HVAC
Satisfied Customers: 163
Experience:  your air.
Type Your HVAC Question Here...
jj is online now
A new question is answered every 9 seconds

On an ecoTEC 618, Im getting F.61, described as "Gas-valve

Customer Question

On an ecoTEC 618, I'm getting F.61, described as "Gas-valve control defective" with a cause of "Short circuit/earth (ground) leak in cable harness to gas-valves, gas valve assembly defective (earth/ground leak from coils), electronic control system defective"

Any ideas?

Many thanks

John Gibbs
Submitted: 3 years ago.
Category: HVAC
Expert:  jj replied 3 years ago.

warmneighbor :

I will be glad to help you if I can. Good morning.

Expert:  jj replied 3 years ago.
How long has the system been running? or is it a new installation.
Customer: replied 3 years ago.

Sorry, just noticed your message above. The boiler has been in about 7 years.

Expert:  jj replied 3 years ago.
the code can be used to verify the controller and vice versa. Either the controller is mistaken or it is doing it's job. We can verify this by using an electric meter. Nothing fancy, just a simple continuity test. Do you have a meter available?
Customer: replied 3 years ago.

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.

Expert:  jj replied 3 years ago.

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.

Customer: replied 3 years ago.

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?

Expert:  jj replied 3 years ago.

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

Customer: replied 3 years ago.

Thank you. Will do. Any possibility of finding a schematic?

Expert:  jj replied 3 years ago.
Here is a link for the manual. I will review it and await your reply. In this way we will be on the same page. I look forward to working with you
Customer: replied 3 years ago.

Thank you. I will get back later. Up to what time are you around?

Expert:  jj replied 3 years ago.
11 eastern standard.
Customer: replied 3 years ago.

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.

Expert:  jj replied 3 years ago.

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

Expert:  jj replied 3 years ago.

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.

Customer: replied 3 years ago.

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)

Expert:  V12Tech replied 3 years ago.
Just a few facts to help here,I recently had the bizarre experience of finding a Coleman gas valve that apparently was "open" when ohm ed for any continuity or resistance etc. I go to my Coleman parts house and get a new one and it too reads open! Every single new gas valve read bad, open, no continuity at all? I found the gas valve has a diode according to the parts house that precludes the gas valve from being assessed in this formerly perfectly fine method. Rather they say if voltage is applied yet no amp draws, it is bad.
Now as to a short in a low voltage control circuit, Don't forget
the Common 24v "neutral leg" of the control circuits Transformer is in fact grounded. So remove the Common or the Ground at least when troubleshooting. The housings of the gas valve will be grounded via the gas line and the utility ground as they are bonded to the unit as well in most cases. Wires typically will be shorted through any penetrations they pass through, pipes they lie upon etc.
You can ground the 24v common just fine. Almost every wire you see will be hot at one point in the sequences of operations except the
24v Common /115 Neutral Both the "leg" or "side of power" that every circuit 24v or 115v terminates to complete its circuit.
I use a 50 to 75 VA rated 24v transformer with a built in 3 amp breaker on the low side so the inline fuse/fried transformer
hassles of troubleshooting are minimized. Essentially I send power to each load isolated and note reactions, then remove any grounds from the commons and neutrals and loop it then test to ground with a analog meter for any movement of a needle whatsoever, any reading is continuity to ground ,digital meters will never be as good for this type of work in my opinion, hope this helps.
Customer: replied 3 years ago.

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)

Expert:  V12Tech replied 3 years ago.
am sorry if I misread, I thought I saw 24v, It is the same protocols regardless, I do not actually know if that is 24v though. I might have misread this .
Expert:  jj replied 3 years ago.

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

Customer: replied 3 years ago.

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).

Expert:  jj replied 3 years ago.

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.

jj, HVAC Mechanic
Category: HVAC
Satisfied Customers: 163
Experience: your air.
jj and 4 other HVAC Specialists are ready to help you
Customer: replied 3 years ago.

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!)

Expert:  jj replied 3 years ago.

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. my contacts are available there.

Warm regards!

JustAnswer in the News:

Ask-a-doc Web sites: If you've got a quick question, you can try to get an answer from sites that say they have various specialists on hand to give quick answers... seen a spike since October in legal questions from readers about layoffs, unemployment and severance.
Web sites like
...leave nothing to chance.
Traffic on JustAnswer rose 14 percent...and had nearly 400,000 page views in 30 days...inquiries related to stress, high blood pressure, drinking and heart pain jumped 33 percent.
Tory Johnson, GMA Workplace Contributor, discusses work-from-home jobs, such as JustAnswer in which verified Experts answer people’s questions.
I will tell you that...the things you have to go through to be an Expert are quite rigorous.

What Customers are Saying:

  • You did one super job of explaining to me everything there is to know about this fridge. I'm looking forward to asking you questions in the future. Jimmy Bagley, IA
< Previous | Next >
  • You did one super job of explaining to me everything there is to know about this fridge. I'm looking forward to asking you questions in the future. Jimmy Bagley, IA
  • Wonderful service, prompt, efficient, and accurate. Couldn't have asked for more. I cannot thank you enough for your help. Mary C. Freshfield, Liverpool, UK
  • This expert is wonderful. They truly know what they are talking about, and they actually care about you. They really helped put my nerves at ease. Thank you so much!!!! Alex Los Angeles, CA
  • Thank you for all your help. It is nice to know that this service is here for people like myself, who need answers fast and are not sure who to consult. GP Hesperia, CA
  • I couldn't be more satisfied! This is the site I will always come to when I need a second opinion. Justin Kernersville, NC
  • Just let me say that this encounter has been entirely professional and most helpful. I liked that I could ask additional questions and get answered in a very short turn around. Esther Woodstock, NY
  • Thank you so much for taking your time and knowledge to support my concerns. Not only did you answer my questions, you even took it a step further with replying with more pertinent information I needed to know. Robin Elkton, Maryland

Meet The Experts:

  • Phil


    Mechanical Engineer

    Satisfied Customers:

    Retired HVAC/ Electrical & Boiler contractor. Industrial
< Last | Next >
  • Phil's Avatar


    Mechanical Engineer

    Satisfied Customers:

    Retired HVAC/ Electrical & Boiler contractor. Industrial
  • gotoman for ac's Avatar

    gotoman for ac

    HVAC Technician

    Satisfied Customers:

    51 years of experience install design and repair of all makes and models of AC
  • Rick Mather's Avatar

    Rick Mather

    HVAC Technician

    Satisfied Customers:

    35 years experience, HVAC
  • Matthew's Avatar


    HVAC Technician

    Satisfied Customers:

    14 years experience in the HVAC field of service, installation, Manual J & D calculations
  • Kenton Guidry's Avatar

    Kenton Guidry

    HVAC Technician

    Satisfied Customers:

    12 years install/service experience.
  • Rick Ridley's Avatar

    Rick Ridley

    UK Heating Engineer

    Satisfied Customers:

    Retired But have had 30 years on the tools, Ex CORGI
  • Tom's Avatar


    HVAC Technician

    Satisfied Customers:

    16+yrs HVAC/R service. Residential Commerical Industrial