Heater won't come on when temp drops...must reset limit switch every time.
Have replaced thermostat and had serviceman check out heater. Said limit switch ok and could find no problem. But something is clearly wrong...should not require manual re-setting of limit switch every time. Also, heater then turns off pre-maturely, and won't kick back on.
Re: heater won't come on when temp drops...must reset...
The over limit switch is kicking on because something is blocking the flue, probably the insulation that goes from the adapter from the wall heater to the flue termination plate... Best bet!! Take off the wall heater cover and light a couple matches and blow them out next to the intake on the top of the heater, it should **** the smoke right up the flue and if it doesnt it is blocked by something like i said earlier...
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Re: heater won't come on when temp drops...must reset...
The limit switch is shutting off and you are having to press the re-set button, right? The limit switch, if I am understanding you correctly, is the thermal disc type, may be ok, but what is causing it to shut off? I would first, not put total faith in the serviceman (PG&E maybe) and replace the limit switch. Its only a few bucks,and easy to do. Then if its still the same problem, look into the venting pipe. As it may not be adequate for the heater. Espically if its new. These new wall furnaces are kind of touchy. It may be larger, BTU wise, and the vent pipe may need to be enlarged. If this is a big job, and a bit too impractical, check the vent pipe, make sure its in good conditon, no leaks ect. install a cO2 detector and by-pass the limit switch.
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HL2 = High limit switch 2 is open. The switch opens if water temp inside the inlet/outlet header exceeds 135 - 140 F.
If you reset the heater and the HL2 does not reset, then the HL2 is likely faulty. When you order a high limit, there are 2 types on these models. Red (135 F) or black (140 f).
If you reset the heater, the HL2 resets and the heater fires for a short time, then the problem is likely with restricted water flow inside the inlet/outlet header.
Check the Unitherm Governor (thermostat) and the Internal Automatic Bypass Valve.
If you are uncomfortable with this type of repair work, a good service technician can be a wise investment in not only your time but the safety of you and your family.
temperature T3 in
wash block CHDESIN
within 60 minutes
Temperature limiter F2 has
Reset temperature limiter F2. See
Resetting Temperature Limiter F2
(Thermostat), 030 4.2. If necessary,
replace the temperature limiter. See
Replacing Temperature Limiter F2
(Thermostat), 030 4.3.
Heater elements do not heat
Check heater elements. If necessary,
replace a faulty heater element; see
Heater Element Replacement, 030 4.5..
Heater level switch does not
See Heating Level Switch Does Not
Switch On, 050 3.1
Voltage (6VDC) from the
electronic not present. The
heating level switch controls
the heating relay voltage.
Check plug connections.
Check electronic module output voltage;
see 070 Fig. 5, Pos. 9.
I want to give a simple explanation before I go any further. On the heating side of a unit even though tthe temp has satisfied the thermostat, the fan will run until it cools down the plenum where the air flows from the air handler. There is a bimetal switch called a fan limit that operates the blower when the plenum reaches the temp set on the fan limit switch. Now if your fan keeps running even after the plenum chamber has cooled down, then you could have a fan limit switch that is stuck in the run position and must be replaced in order to correct the problem.
If the unit comes on and runs but then shuts down, that sounds like an indication of a high limit trip.
Most, if not all, furnaces have high limit switches that keep a constant check on the temp inside the furnace or air handler. On most systems, once this high limit switch has been made (got to hot), the limit switch breaks control voltage to the heating device (strips, gas, fuel, etc.etc..). The blower motor continues to run until the high limit has dropped in temp and reset itself.
On some models, the high limit is a manual reset, meaning you need to reset the switch yourself or shut the unit off and then back on to reset it.
Check all filters and replace as necessary. Check the coils and fan blades for dirt build-up and cleanliness. Check motor belt (if applicable). If all these fail to solve the problem, then your issue either lies within the blower motor itself not moving enough air for proper heat transfer. Or the high limit switch itself is failing.
the high limit and low limit are set in the configuration part of the thermostat. you can find out how to get into it with your installation manual, NOT THE OWNERS MANUAL. Or in order to help, someone will need the model # of the stat, because every one is different.
Tjere is a limit switch that will only allow the durnace to reach a certain temp by kicking on the fan. The thermostat being unable to read the temp affects its ability to keep the furnace from exceeding your settings. *Advise not to use until corrected. Both limit switch and thermostats are inexpensive and simple to change. If in doubt, call a heat and AC tech to repair.