The circulator pump on my boiler is controlled by a line voltage thermostat, which runs on 120v AC as opposed to 24v like most HVAC thermostats do. Last night I did some work with a 120/24v transformer, so that the line voltage thermostat will send a signal to my HVAC fan to kick on at the same time the ciculator pump turns on. The problem I have, is it seems the line voltage thermostat doesn't put out a constant signal. It cycles, so when it kicks in, it runs the pump (and HVAC fan) for 10 seconds, then shuts off for 10 seconds, then kicks back on for 10 seconds. Even taking the transformer out of the circuit, it does the same thing to my water pump, cycling it on and off. I've verified this with a volt meter and can watch the outgoing signal jump to 120V, then back to nothing, then back up. So, is this normal, or is my one year old digital thermostat already toast? It's technically a thermostat for electric baseboard heat, which I would think would need a constant signal to heat the elements.
So is the thermostat new and do you have the paper work with it? I see you said it was a year old has it worked fine up to now?
A quick search and I found that some do cycle off and on when temp is reached, a look through the directions should tell you if that is what you have maybe.
It's worked in the past, but I think it was still cycling the pump on and off. Water holds enough heat that even being pumped a few seconds at a time it still would heat the house fine. The water only has to travel about 5 feet before reaching the heat exchanger in my air ducts. And it wasn't cycling when it reached the temp. If my house was at 70° and the thermostat was set at 70° there wasn't a current. But if I set the thermostat to something higher, such as 75°, it would just cycle every 10 seconds or so. I don't have the paperwork, but I do have the box and couldn't tell anything from that. Maybe I'll see if I can download a pdf but either way it looks like I need to find another thermostat.
I found a Honeywell that looks identical to mine, down to the injection molded casing and LCD screen. The instructions for it says in default mode it turns on and off every 15 seconds for baseboard heat, but there's a function to change this to 15 minute intervals for heaters with blowers. Unfortunately mine doesn't have the switch in it to change it to the 15 minute setting, but it's making me think my thermostat is not broken, but working perfectly. It's just not perfect for my needs.
Sounds like you need a standard 24V HVAC thermostat with a 24v coil relay for the pump. Use a set of contacts on the relay to power the pump w/120, and the blower will run normally off the control voltage at the air handler.
Something like this? http://www.amazon.com/Supco-General-Purpose-Current-Contacts/dp/B004XS148C/ref=pd_cp_hi_0 Now that you mention it I do remember looking into using a relay last winter, but I was a little confused looking at the specs of the relays and at the time I took the easy route of using a line voltage thermostat to run my pump, and then just ran my HVAC blower 24/7. Now I'm sick of hearing the fan running all the time and hope to find some energy savings by having it off as well.
How big is your circulator pump? I'd probably go a bit bigger in the current size - in rush will be a bit more on a pump than a fan. If you couple that with a split-system digital t-stat (one for furnace and AC) wire the furnace contacts to the 24Vcoil and run your 120 on the output contact, you'll be in business http://www.amazon.com/Ssr-25da-Temp...&sr=8-7&keywords=24V relay&pebp=1416333084306 you may have to wire the coil in series with the power to your air handler control board
probably won't be necessary - I was thinking if it were a true split system, modified with a hot water HTX. The control board at the air handler will time delay the fan to kick on 10-15secs after a furnace fires and run 30secs after the furnace turns off. Not knowing what the true original setup was/is on the air handler. If it was an electric heat system, wiring the heat switch(white wire typically) in series with the coil will kick the pump on and then power at the board will run the time delay for the fan. Some digital t-stats actually have some of these time delay features in them as well, you can adjust the programing if you read a bit deeper into the manual
You could parallel it in as well running a two conductor to the relay, wiring one side to the white and one to ground. Or you can series it with one side to white and connecting the other to the normal heat wire(should be white but could be any color) going to the air handler.
I'm lost as normal, wiring across the coil in series is going to give you a voltage drop to the control board or am I not understanding what you are doing.
No spark your not lost. That relay that I posted in the amazon link is a solid state relay - won't pull anything for amperage or voltage drop. Parallel or series will/should have the same effect. I'm just not 100% sure about what the control board at the air handler in this system is doing - some use the heat relay from the t-stat to drive the fan on/off in the auto setting, the fan wire(yellow?) is for your manual ON(that's what I recall anyways). That make sense?
Thanks for thoroughly confusing me with all that series vs parallel talk! I understand DC pretty well, but AC is much tougher for me lol. Anyway, I figured out that my Aube thermostat for the water pump is actually made by Honeywell (or vice versa) and found instructions to change the setting of heat cycles from 15 seconds. After some wiring trial and error I got the transformer to work to so it kicks on at the same time as the pump. The problem though, is that the “long” cycle on the thermostat is 5 minutes, so everything runs for 2 ½ minutes and then kicks off for 2 ½ minutes. This is unacceptable since it takes twice as long to bring the house up to temp, and will probably burn out my fan and kill my energy use at the same time with the blower having to start so often. So right now I’m on the search for a programmable line voltage thermostat that doesn’t work in heat cycles. If I can’t find one I’ll just get a 24v programmable thermostat and use a relay like suggested. Thanks for the suggestions, I never even considered that my thermostat was designed to work in cycles like that!
So what is the rest of the system originally set up for? Is this a AC system with forced hot air or just forced hot air system with a boiler, pump & heat exchanger?
I’ve got a boiler, pump, and heat exchanger. I’ll try to explain and hope it makes sense. The house has a heat pump/AC unit with electric back-up, which is controlled by a normal 24v thermostat. Once temps drop below 45° I turn off the heat pump and only heat with wood. Next to the heat pump in the basement is my wood burning boiler. Water is circulated from the stove up to a heat exchanger in the air ducts, so as air is blown out of the HVAC unit it immediately picks up the heat from the heat exchanger and moves the warm air through the air ducts. Upstairs I have 2 thermostats, once controls the heat pump/AC unit, and the other is the line voltage thermostat that controls the water circulator.
