teledyne laars mark v does not fire up

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M

mnschu

0
Aug 17, 2011
22
San Jose, CA
I have a Teledyne Laars Mark V pool heater that has stopped working.
Here is more info:
Moved into the house about 1 year ago.
The last time we used the heater was about 4 months ago, it worked fine and fired up.
Gas to heater has been turned off over the summer.
Tried today to fire it up and use spa, but did not turn on.
Pilot light will light up and stays lit.
I tried flicking ON switch several times, but did not work.
Normally, when I flick the ON switch I hear the gas valve open and fire up pretty quickly.
In the past, when I flick the ON switch, sometimes it did not fire, but I turned off, wait a few seconds, and flick on, then it fires.
So it may have been an existing problem.
I am looking for advice on what to try to isolate the problem.
Is there way to override the control circuitry to force it on?
I read a previous post where the poster did this, but not sure exactly how this control unit works.
There are 4 wires going to the gas control. I do not know how this works, but is it like this:
2 wires go to thermocouple. Does this get heated by pilot, and presents a voltage to gas valve when hot, so must be hot for gas valve to work? Can I override by using some battery?
2 wires go to the thermostat temperature control (has dial from low to high) box. This box has a switch. Also, it seems to have some thermocouple that is in line with the water. I am guessing the dial from low to high is just a rheostat. Could something be wrong in this control box? What is easiest way to test?
Could the gas valve be bad? How to I confirm?

I would like to determine the problem and replace or fix the part.
Any advice is appreciated.

Thanks,
Michael
 
I was doing some more investigation and have some updated info and pics.

Pilot light:
I believe the pilot light is not working properly.
The fire comes from the bottom holes, I think that is where the air is supposed to be mixed with NG.
It seems my pilot is plugged or something is preventing it from lighting at the top.
I can't see how to remove this, space is tight and not easy to get access to, so how to I fix or replace?
See pic below:

[attachment=1:3vzjevfb]pilot.JPG[/attachment:3vzjevfb]

My gas valve looks like this:
[attachment=0:3vzjevfb]gas valve.JPG[/attachment:3vzjevfb]

The two terminals at the top connect to the thermocouple at the pilot light.
The two terminals at the bottom I believe connect to the thermostat control box, but I can't confirm as the wires get hidden.

Some experiments I did:
I measured the voltage at the thermocouple pilot light terminals, it was only about 5mV.
I tried using a 9V and 3.6V battery, shorting these terminals, but no luck. I tried in both polarities.
I also tried with and without the wires connected.
Is this voltage too great? Or do I have more than one problem. I hope I did not damage anything with this high voltage.

I tried heating the thermocouple manually, using a propane torch (kind used for soldering copper pipes).
I was able to apply the flame to the top part, but still did not turn on.
After applying the heat, and then turning off the torch, I measured the voltage as fast as I could at the terminals.
It was about 70mV and dropping fast.
What voltage does the gas valve expect when pilot light is lit?

I have no idea how to test the other terminals that I believe go to the thermostat control box.
How do these operate, on a voltage or resistance?

Appreciated any help or suggestions.
Thanks,
 
That orange flame is the key. It should be blue and stronger. My first expectation would be the pilot jet is clogged with corrosion. The blue flame is hotter, making the pilot generator (your thermocouple) create a higher voltage. The current from this travels the safety circuit of temp limits, pressure switch, thermostats, and possibly a fusible link.

You cannot bypass your failure.

That looks like original equipment so that makes it pretty darned old. Jandy bought Teledyne quite a while ago. I have no docs but replacing the pilot assembly looks to be in order.

Scott
 
Thanks for the link Paul!
They had a link to the manual and I was able to troubleshoot my problem as being caused by the thermostat.

Here is where I am at so far:

I could not unscrew the pilot assembly near the burner/pilot light area.
I could only unscrew the connection near the gas valve.
So I decide to try to clear it out using compressed air (cans used for dusting electronic equipment).
I shot some into the pilot light pipe, and then reconnected the pipe to the valve.
I turned gas on and voila! This was enough to clear out any debris, and the pilot burns from the correct location in the top, and is blue.
I measured the voltage at the valve terminals for this pilot light thermocouple, and it is now 575mV, close to what the manual says it should be 600mV.
So now my pilot light and thermocouple are working.

I now follow the troubleshooting guide in the manual, and start bypassing all the safety/trip control circuitry.
I determine the thermostat is not working. If I bypass this, the gas will fire up and heater works.

I open up the thermostat control box, and test the switch, it is working properly.
As I move the temperature knob, I notice a plate move closer and farther away from something that looks like a relay.
I am guessing this plate is a magnet, and connected to a thermostat similar to those used in cars.
I guess as the metal in the thermostat expands or contracts based on temperature, this plate moves closer or father from the relay.
I take a screwdriver, and push this plate closer to what looks like the relay switch, visually it does not even look like the plate moves, so maybe I am moving it about 1/16th of an inch. This is enough to fire up the heater. If I take pressure off the plate, it moves a bit farther from the relay, and the heater turns off.

The link with parts for sale only has the whole temperature control assembly for sale, and it is $152. Does not seem practical for this old heater.

Does anyone know of a way to fix this and recalibrate the thermostat control?

Thanks,
 
Seeing as you have 575 Mv then you do not have a thermocouple but, instead it is a power pile (sometimes refered to as a power generator or thermopile). A good powerpile will put out 750 Mv. 575 is on the low end of being good. Before you change it out though I would suggest you clean all connections thru the system. Any small amount of corrosion can cause voltage drop and 750Mv is not much to begin with.

The sketch below shows how your system works. The powerpile generates a small current. That current goes out thru all of the various sensors and switches in the system including the thermostat. If all of these switches are working properly (ie: closed) then the current will get back to the gas valve and cause it to open. The voltage is critical as this is a 750 MV gas valve +- ~100Mv. If you are not sure if it is the valve or the switches there is an easy test to do. On the gas valve you noted there are 4 wires the should be connected as follows: One to the TP terminal, one to the TH terminal and two to the TP/TH terminal. These may be labeled as something else. If you coect a jumper between the two single wire terminals you will bypass all of the safety switches and the thermostat. If the powerpile is good (in a flame and puting out good voltage) and the gas valve is good then the burners will fire up. If it does not fire up then you either have a bad gas valve or too low of a voltage from the powerpile. (600 MV seems to be the low end for a gas valve to work

gashtrmillivolt2.gif
 
mnschu said:
Thanks for the link Paul!
They had a link to the manual and I was able to troubleshoot my problem as being caused by the thermostat.

Here is where I am at so far:

I could not unscrew the pilot assembly near the burner/pilot light area.
I could only unscrew the connection near the gas valve.
So I decide to try to clear it out using compressed air (cans used for dusting electronic equipment).
I shot some into the pilot light pipe, and then reconnected the pipe to the valve.
I turned gas on and voila! This was enough to clear out any debris, and the pilot burns from the correct location in the top, and is blue.
I measured the voltage at the valve terminals for this pilot light thermocouple, and it is now 575mV, close to what the manual says it should be 600mV.
So now my pilot light and thermocouple are working.

I now follow the troubleshooting guide in the manual, and start bypassing all the safety/trip control circuitry.
I determine the thermostat is not working. If I bypass this, the gas will fire up and heater works.

I open up the thermostat control box, and test the switch, it is working properly.
As I move the temperature knob, I notice a plate move closer and farther away from something that looks like a relay.
I am guessing this plate is a magnet, and connected to a thermostat similar to those used in cars.
I guess as the metal in the thermostat expands or contracts based on temperature, this plate moves closer or father from the relay.
I take a screwdriver, and push this plate closer to what looks like the relay switch, visually it does not even look like the plate moves, so maybe I am moving it about 1/16th of an inch. This is enough to fire up the heater. If I take pressure off the plate, it moves a bit farther from the relay, and the heater turns off.

The link with parts for sale only has the whole temperature control assembly for sale, and it is $152. Does not seem practical for this old heater.

Does anyone know of a way to fix this and recalibrate the thermostat control?

Thanks,
Click to expand...

There is no known way to calibrate it. Yes you could bend it some but you are still just guessing. You are pretty much stuck with purchasing a new one. It's a gamble when a unit gets a certain age as to whether or not it's worth investing money into it.
Also, if you did get a new unit it would have a digital readout and you would know what the exact temperature you are running at.
 
I received the new thermostat and thought it would be a simple part replacement.
However, I discovered the dimension of the thermostat would not fit into my existing temperature control enclosure.
I guess my model is older and they slightly changed the enclosure, making it a bit bigger in newer models.
By drilling a few holes and some minor modifications, I was able to make it work!
So what I thought would take me an hour took a good half day.
The temperature dial is at a slight angle, but it is working now!

My advice on anyone with an old heater like this, upgrade to something newer and don't spend too much time on repair.
I think I will start looking on Craigslist for used pool heaters, seems to be people filling in their pool from time to time on there selling their equipment. Maybe time to see how much I can get from scrap metal in the old Laars Mark V, must be a lot of copper in there. :)
 
You might get $40 for the entire unit, that includes the copper which you would need to cut out in order to get a decent price on it. Be careful on purchasing a used heater. Just keep in the back of your mind what you just went thru to fix the one you have. With a used heater you could inherit someone elses problem. Also, if the heater isn't hooked up, how would you plan on testing it before you purchased?
 

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