I have a water boiler with an external pump and an internal transformer as my heating source, controlled by a Honeywell programmable thermostat. The PROBLEM: #1. When I turn on my heat, the PUMP will NOT START sometimes! At times, it WILL START and run! Sometimes it will start but cycle off after 10-15 minutes! When it doesn't start or cycles off, the only way to start the pump is to turn ON and OFF (sometimes repeatedly) the MAIN power switch to the system! Problem #2. I have replaced my TRANSFORMER TWICE because they melted (the plastic where the terminal screws are). I thought maybe the internal heat was the problem so I leave the door ajar to allow heat to escape! This is my second winter with this transformer and seems to be holding up with just a small amount of melting! Thanks AL

The pump is controlled by a relay. I don't know if it has a delay like forced air, but the intermittent problem likely is the relay. You may want to look at the transformer. It is possible it is not big enough to handle the gas valve, the pump relay, the ignition, any zone valves, anything else the system needs to start up. If the inadequate transformer isn't putting out a full 24 volts, that could cause the relay problems too. If you have a volt meter, the first thing I would do is check the voltage at the transformer when the system kicks on. If it drops below 24 volts more than momentarily, either the transformer is too small, or something is drawing too much current. You could add up everything connected on start up and compare it to the rating of the transformer. The devices should all be marked with an amperage or watts. Multiply the amps by 24 volts to convert to watts. If the total is as much or more than the transformer, replace it with a bigger one. If less, try to check each device for excessive current. Heating up is a sure clue.

I would also add a fuse for the transformer. They are cheaper to replace than transformers.

Thanks for the info. I will try your suggestions. I'm going to try attaching some pictures of system!

AL