These are used in gas water heaters. The plunger pulls back to allow
gas to flow when 3V is applied. I have 5 which have failed. When I
apply 3.27V regulated to them I have to gently push the plunger for it
to retract. Then it is OK and hard to pull out as it should be. When I
turn off the power it pops out OK. It has continuity between positive
and negative leads, about 5.2 ohms. There is also a yellow control
wire in addition to the other 2 wires. When I test continuity between
the yellow control wire and the other leads the multimeter does not
beep for continuity but reads 320 ohms. Is it measuring impedance?
You seem to be talking about the "thermopyle" powered solenolds.
"Consumers" really should not mess with these. If the thermopyle doesn't
put out enough juice to operate them, the solutions are: 1) ensure the
pilot light is properly adjusted; 2) replace the thermopyle (they are
relatively cheap); or call in a technician to service the gas valve
If you W/H doesn't have a pilot light most comsumers should just call in a
tech. Many of these non-pilot light appliances operate directly on 120
volts and include a "flame detector."
They typically last DECADES without any attention although I had an "infant
mortality" situation with a clothes dryer.
I haven't seen a single one of these where the solenoid is expected to
pull back the plunger. They have all used the manual "push and hold"
button to move the plunger into place - all the solenoid has to do is to
hold the plunger in that position, whilst the flame is present. Once the
flame goes out, so does the plunger.
The electrical power generated by a pyro-electric flame sensor is pretty
low, I wouldn't think it would ever be enough to actually retract a
I did come across one where the only fault was that the control valve
assembly had moved back a fraction of an inch. So the push button was
"bottoming out" on the carcase without having moved the plunger fully
home. So nothing more was required than move the assembly back to where
it had been. This had defeated the "engineer" called in to fix it, who,
having replaced the flame detector with no improvement, had declared
that a whole new water heater was needed as the control valve unit was
no longer available but needed replacing..
There is no pilot light. There is no push button. When water flows a
switch is opened and this fires the solenoid to allow gas to flow. It
is not a thermopyle whatever that is it's just a simple 3V solenoid.
The solenoid does pull back the plunger.
There you go, you see. A bit more information helps to replace the
assumptions that will otherwise fill the void.
So, to return to your original question. You apparently have one winding
with a DC resistance of 5.2 ohms and another winding with a resistance
of 320 ohms. Your test meter almost certainly measures DC resistance.
You don't mention whether the solenoid is coupled to the gas valve when
you carry out your test. If so, it could be the valve that is too stiff
to move. With a couple of watt solenoid, there isn't a great deal of
The sense wire is used by the controller to check whether the plunger
is in or out. It won't affect the basic operation. I would forget about
it, for the time being at least.
You don't mention how long it took the previous 5 to fail. Did they work
for a while and then fail? Or did they fail, right out of the box?
Solenoids are extremely reliable as a rule - which is why they are used
as interlocks in many safety-critical situations. One cause of failure
can be over-enthusiastic or inappropriate lubrication of the plunger.
Another can be mounting at an angle not designed for. eg most of the
problems are from misuse, rather than being inherent.
So, lacking further information, I assume that the solenoid is actually
coupled to the gas valve when you carry out these tests and that the
fault lies in the gas valve, rather than the solenoid. However, more
facts may discount this hypothesis.
It is powered by a 3.3V regulator. Originally it was powered by 2 x
1.5V batteries. It is definitely the solenoids that have failed there
is no gas valve. The plunger retracts and gas flows through the gap.
My original post explains how they fail. They work for a few years
Was this system originally designed to operate with a fixed 3.3V
regulator? Or 2 batteries? Either of these seem like a pretty unusual
system. Nothing like what I've ever seen.
Here's my guess: The coils were originally intended to operate off of a
thermopile. While its open circuit voltage may be a couple of volts,
under the load of the solenoid, that will be reduced, as will the
current. Somewhere along the line, someone made a re-design (or a hack)
and ran the same coil off of batteries. The coil, not being designed to
run off of such a source, is now suffering from reduced life.
Paul Hovnanian mailto: snipped-for-privacy@Hovnanian.com
No the califonts originally took 2 X 1.5V batteries. I removed them
and hooked up 3.3V regulators instead. This has worked well for a long
time. Could the fixed 3.3V cause a problem as opposed to batteries?
The voltage under load is 1.57V using the fixed 3.3V input. All the
voltage and resistance measurements I have given are the same on
faulty and working solenoids.
Several things spring to mind. The first is that this solenoid, from
your figures, would have been taking about a half an ampere hour from
the batteries. For a system where the solenoid could be needed to be
engaged for many hours a day - this was hardly likely to be a successful
Next, from your latest description, this isn't just a solenoid - it is
an electrically operated gas valve. There must be gas-tight seals
involved somewhere. If these seals are around the plunger, it may be
increased stiction with these seals that is causing the problem. This is
easily proven - use a force gauge to measure the force needed with an
(unenergised) new valve, compared to one that has "failed". If the force
is greater with the old valve, the problem isn't electrical, it's
If that is the case, then "a few years" may be the design life for these
valves, when used with gas. Gas does tend to be much harder on seals
than, say, light oil. These valves may have been primarily designed for
the latter, although also rated for gas.
If the force gauge reads the same with old and new, then there is one
other possibility - permanent magnetism. It could be possible, for a
number of factors, for part of the magnetic loop to have become
permanently magnetised, in opposition to the energising magnetic field.
This can be proven by reversing the power supply connections, but don't
do this with the sense wire connected! The solution to this is easy -
"degauss" the solenoid. This is normally done by placing the object in a
strong AC magnetic field and slowly reducing that field to zero
(typically by slowly removing the object from the field).
All there is is a solenoid plunger with a spring and small round
rubber seal on the end which covers the gas inlet hole. The problem is
with the solenoiid alone - I tested them all in isolation, removed
from the system. The plunger moves freely in all cases.
I have tried reversing the inputs and it just does the same thing, i.e
needs help to retract and then pops out when the power is turned off.
What am I looking for if I reverse the connections and there is
I have exposed part of the core and put a small screw near it. I feel
no pull or push. I also tested one solenoid with the spring removed
and it worked suggesting that the magnetic field has weakened or has
an opposing permanent field. Where do I find a strong AC field and how
do I reduce it to zero?
> I have tried reversing the inputs and it just does the same thing, i.e
> needs help to retract and then pops out when the power is turned off.
> What am I looking for if I reverse the connections and there is
> permanent magnetism?
I have combined your two posts to answer them together.
If reversing the input doesn't produce a change then it isn't a
permanent magnetism problem. The permanent magnetic field that hindered
with one connection would actually assist with the reverse connection.
However, for academic interest:
As to the strong AC field- your local scrap dealer may have a one
hanging from a crane. Good blacksmiths have one. You can buy
"demagnetisers". Or, it is possible to make one.
To reduce the field to zero, you either connect it to a variac and turn
that down or, even easier, slowly move the item further and further from
But back to your problem - what you need is a working one and a
non-working one side by side. Swap the springs. If that transfers the
problem, then you know that it is the spring. As you have discounted
permanent magnetism effects, a change in spring properties is the next
Ok this is rather embarrassing. But not my fault! Our maintenance guy
had written dud on all the solenoids but he tested them outside the
califonts. Turns out they need to be in place with the spring already
partially retracted to work. Also he tested one or two in place but
the machine may have had a faulty control board and the sensor wire
may not have been working. Thanks to all who replied and sorry for the
waste of your time.
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