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eastwood 03-10-2008 05:57 PM

Parts of a boiler/hydronic heating system
I have a boiler in my basement that recently stopped working. I went without heat for about two weeks when I had enough and decided to fiddle with it to see if I could correct the problem. (it wasn't bad enough to spend $100 on a service tech) The whole setup seems pretty simple, however I don't know the correct terms for some of the pieces so please bear with me.

I see the electric shutoff switch which supplies power to the whole system. One of the items off this switch is the pump motor. The curcuit for the pump is run through some sort of low voltage on/off relay switch which seems to be triggered (on and off) by the thermostat in my living room. I just noticed it buzzing which it hasn't done before. I bypassed it and hardwired the pump to the switch and it it worked wonderfully. After a few hours I decided to check the pump and it felt very hot. I wasn't sure if the motor itself gets hot or if the 180 degree water circulating through it caused it to be hot. I turned the whole system off for about eight hours and let it cool. I then turned the pump back on but left the boiler off so it was only circulating cold water. Again, after a few hours I checked it and it was pretty hot.

Is this normal? Can I theoretically leave the pump on all day and night until I get the new transformer/relay thingamabob? I wasn't sure if this was a good practice or not. The thermostat still controls the boiler so if the right temp is reached the pump will still circulate water regardless if it's being heated or not.

Also, there are two mercury rocker switches on my boiler. One is obvious enough...I can select how hot I would like the water in the boiler to be. The other one is a little bit beyond me though. It sits in the line bewteen the pump and the main electric switch. It looks like a mercury rocker switch with a magnet at the bottom. I guess if electricity is applied it would pull on the magnet and cause the murcury rocker to close/open. I simulated the magnetic pull and just tipped the rocker with my finger. Nothing happened. No clicks or hisses. Does anyone know what this rocker switch is for? I don't see any extra wires that would control the magnetic device.

And last, for now, that transformer/relay thing that either completes or breaks the circuit for the pump...does anyone know the correct name of that part?

Thanks In Advace,

glennjanie 03-11-2008 02:03 PM

Hello Jim:
The relay device is just that, a relay. To be safe, you should take the old one with you when you go after a new one. I suspect the second mercury swithch is some sort of safety sensor. Your pump motor sounds like it may have bit the dust, but you might try oiling the motor and see how long it will run. Don't use WD-40, it will burn it out quicker. You need a small bottle of oil with an exdender spout on it and about 3 drops in each end of the motor is sufficient. Your impeller on the pump may also be badly worn so, it would be best to replace the whole pump. There are usually 2 bolts above the pump and 2 below it on flanges; so its a fairly straightforward change out.

guyod 03-11-2008 07:40 PM

I had a circulator pump that stayed on all the time. It got really hot but It lasted all winter then i sold the place. they are only like $100 and easy to replace like Glenn said. so if your tight on money or just dont want to replace hydro-stat( think thats what its called) Its a pain you have to drain the system to do it. if you roll the dice and let it go odds will be in your favor it will last the rest of the winter.

eastwood 03-12-2008 02:21 PM


Originally Posted by glennjanie (Post 16848)
Hello Jim:
The relay device is just that, a relay. To be safe, you should take the old one with you when you go after a new one. Glenn

Thanks Glenn,

I did bring the relay with me but most of the electrical shops in my area didn't even cary relays to begin with. The ones that did didn't know anything about them. I tried a heating/cooling shop but they won't sell to individuals. I finally found what I needed at Grainger. The rep at the front desk was nice enough but still didn't seem to know how to match up what I needed. He gave what he thought was the best match but I'm not so sure. I had a 3/4 H.P. relay before but the one he gave me is a 1/2 H.P. Is that going to make a big difference? Should it work at all? What does the H.P. affect?

I got it home and hooked it up (it was very straightforward) but again all it did was hum. I do know the old relay was bad because when I took it apart some plastic pieces fell out so I'm still hoping there isn't any trouble anywhere else. I tested the low voltage leads that power the relay and they supply 25.6 volts as they should.

While sitting here I just notice that the box the new relay came in says

12A CONT.@ 125VAC

I don't see anything that has anything to do with low voltage although the two relays looked identical. Is the box stating the coil sould be powered with 120 volts...?

Also, guyod, thanks for giving me the heads up on how your pump worked out.

glennjanie 03-13-2008 07:50 AM

I'm pretty sure the coil should be 24v. That may be why you only get a hum from it when you turn it on.

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