Teledyne Laars LLD - another won't fire-up post

[bandersesk]

Hi,

I have a Teledyne Laars LLD heater running on natural gas.
It would not fire up when I opened the pool for the season.
It last ran in June 2015.

Manual gas valve open. Checked 24V fuse. 24 volts at the fusible link, etc.
It's not the pressure switch, it was a problem in the past, and I knew to check it.

I don't here the 'click' of the gas valve opening. No smell of gas.

In the process of pulling out the manual!

I think it is using the igniter as the flame sensor and never been 'rectified'.

I plan on opening the side panel to see if the igniter is glowing.

Question - does the temperature sensor ever go bad? Is it a thermistor or a thermocouple?

Any other items to look at?

Thanks!

 

[ps0303]

If you don't here the gas valve click then it's not even getting to that point of the process.

This unit should have a separate flame sensor but your' not even get ignition yet.

Yes the temp sensor can go bad.

I would check all of the sensors including the limits on the header.

 

[bandersesk]

Is the temperature sensor (used for temperature control) a resistance device, like a thermistor, or is it a junction device, like a thermocouple?

https://premium.zodiacpoolsystems.com/~/media/c678e162f9c248908bf428f8ab038855.pdf

 

[ps0303]

Thermocouple is for the ignitor and keeps a milivolt system powered.

Yes your dials are a rheostat for setting the temp. Then the thermistor monitors the water temp. So your dials on the unit could go bad.

 

[bandersesk]

I don't know how I fixed it, but it is done.

I went through some basic trouble shooting. In the process, I was disconnecting sensors, switches, etc. to measure ohms, volts, and whether they were open or closed.

I felt better after I shut off the gas, disconnected the gas valve, measured resistance, and then put 24 volts to it, and heard it snap on and off. Had not heard it yet this season.

At one point, I put everything back together for the evening. The next day, I came out to check the system, turned on the pool pump, and the heater lit up.

No idea how I fixed it - I'm blaming it on humidity or a loose connection and time or fiddling corrected it.

 

[danpik]

A lot of times, especially with milli-volt systems, the connections can get enough corrosion/tarnish to impede the electrical flow thru the safety circuit. The simple act of unhooking and reconnecting the connection points can re-establish a good contact to awaken a system. I have a habit now of using No-ox on a lot of connections on an outdoor systems now and indoor systems in damp basements.