hydro therm residential boiler with 3 zones

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  #1  
Old 10-09-03, 10:21 AM
Kurt Hertel
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Unhappy hydro therm residential boiler with 3 zones

Good day all,
We have the above captioned hvac system in our home. It isn't functioning properly (at all) right now. It is pre electronic pilot. The pilot light is on. Turning up any or all of the thermostats to call for heat results in the circulation pump running and the zone valves opening, but no fire under the boiler comes on. My questions are: How much voltage does a thermo couple generate? Is it a/c or d/c? What is the function of the 'high limit' switch. Does it require voltage of either a/c or d/c ( which?) How much voltage should the gas valve require and what is it's source voltage. I see a strip on the rear of the boiler housing with two wires from the transformer running inside to the gas valve. I measured 234mv dc at the front and rear of this strip. Any more info I'll be happy to provide.Thanks in advance for your help.
 
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Old 10-09-03, 11:37 AM
Ed Imeduc's Avatar
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boiler

Lets try it this way. You say the zones call for heat and they open and the pump comes on ok. Now on the boiler gas valve you did light the pilot and it stayed on. Now you did turn the gas valve to on after that , You did didnt you?. Then I take it that the gas valve should turn on from an aquastat there on the boiler. So you need 24 volts+ to it and then down to the gas valve the other line on the gas valve is the -. So if the boiler is trying to turn on you should read 24 volts there on the gas valve. "So think" the 2 wires off the transformer put right on the gas valve would make it open and light.Let us know what you find there on the valve ED
 
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Old 10-10-03, 06:31 AM
Kurt Hertel
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Ed,
Thanks for the reply. I went home yesterday and checked voltages with my Fluke. I get no voltage from the transformer to the 'strip' I guess I need a transformer,eh? I was looking for 24v a/c correct?
 
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Old 10-10-03, 08:24 AM
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Transformer

24 volt transformer, also look and see if input is 110 or 220. Also look and see what the VA is on it thats voltamps could be like 20, 40 , 50 ,60. ED
 
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Old 10-11-03, 03:00 AM
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Boiler won't light

If you are getting 234mv then I would think you have a combined thermocouple and thermopile system. The thermocouple keeps the pilot going while the thermopile actuates the main flame.
First check that the hilimit is out usually this a small red button on the hilimit stat.
Next check the voltage you get on the gas valve. IF it's under 500mv you could try shorting out the two wires which go up to the boiler stats ( the control stat and the hilimit are usually in series Although in some cases the hilimit can be on the thermocouple circuit.
A break in the circuit up to the stats, A faulty thermopile, or not enough flame onto the thermopile are possibilities.
 
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Old 10-11-03, 03:48 PM
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Pilot on Boiler

OOPs, What I meant was check the hilimit is NOT out,
If the system was not shut down correctly at the end of the last season it is possible the residual heat in the boiler put the hi limit out.
The better way is for a the pump to be wired through a lo limit stat which shuts down the pump when the boiler cools.
The burner should ALWAYS be shut down and the boiler left to cool BEFORE the pump is shut off to avoid this problem.
 
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Old 10-13-03, 06:39 AM
Kurt Hertel
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Well, thanks to all for your responses. Turns out we have a milivolt system with a thermopile. It should generate between 500 and 700mv. Ours was tired. Replaced it and voila heat, etc.
 
 

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