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An Aquastat is a device used in water heating systems. It is used to control water temperature. Aquastats usually have a high limit temperature and a lower limit temperature. If the boiler is heating it will do so until it has reached the high limit and then automatically shut off even if the thermostat is indicating more heat is required. The boiler will come on again if the water temperature falls below the high level range. Similarly when the boiler water temperature goes below the low level point, the boiler turns on to ensure the water temperature does not fall below a certain point and is maintained at one level.
Listed below are a few questions answered by the Experts on issues related to Aquastats.
First, a 20 degree differential signifies the difference between the high limit and the lower limit. The boiler will come on if the lower limit is reached or ceases if the higher limit is reached. Based on your setting of high temperature of 170 and a differential of 20, if your boiler temperature falls below 150 the Aquastat will initiate the boiler to turn on and heat until 170 and then turn off once this temperature is reached. By doing this if your home is heating properly it is considered normal operation of the Aquastat. Short cycling is when the Aquastat switches on and off in rapid succession for no apparent reason without much variance in water temperature.
The main difference between the two Aquastats you have mentioned is the mounting. The older one is a vertical mount whereas the new one is a horizontal mount. The specifications are identical with the two Aquastats. The new one should work with your burner unit unless the mounting affects the functioning in any manner. Another important detail for the new Aquastat you have purchased is it is meant for high efficiency boilers.
First check if the solder connections on the back are loose. Dismantle and check by unhooking all the wires. The Aquastat is not a simple relay which goes on and off. The contacts could get sticky. On rare occasions the cover could be causing the issue, try running it without the cover. The contacts on the circulator relay usually do not corrode but burning is possible though the circulator does not require much of a load. You will need to buy the whole unit to repair this. The other common issue occurs with the soldered connections at the back. You can test for power going through the Aquastat. Test for power between C1-C2 and B1-B2. If there is no power, the problem could be within the Aquastat.
Seems like there could be a problem with the operating control and may need replacement. If the thermostat is sending a signal to heat and if there is no power relayed at C1 and C2, the control could be faulty. Try jumping the thermostat terminals by running a wire across T and TV screw terminals on the control to be sure. If there is still no power at C1 and C2, you can conclude the problem lies with the control.
Aquastat is a delicate device which has its own components as well as is a part of a bigger heating system. It functions to keep a control check on the temperature. Other components too if affected can influence the functioning of the boiler. To determine the issue lies with the Aquastat can be tricky and complicated to an untrained eye. Common problems that may occur with it sometimes can be fixed by a layman with an idea of the mechanics behind it. There may be other major problems which should be tackled by professionals. To get a fair idea regarding the Aquastat issues faced by you, Expert answers, information and guidance will prove useful.