heater runs all the time

[subway41]

we have a gas hot water heater that runs and continues to run once we turn on the power, even when it is above the temperature setting.
we changed the thermostat thinking that that was the problem, but it still runs continually.
Any suggestions would be appreciated.
thanks

[ToUtahNow]

With the limited information you have provided I am a little concerned about giving you any advise. A run-away thermostat can be very dangerous and should be looked at by a qualified serviceman.

Without knowing what equipment you have I can tell you that the control circuit of your water heater is nothing more than a series of normally open or normally closed switches and limits. It is all a matter of finding out which switch is not opening.

Mark

[subway41]

thanks, mark,

I was talking about a gas hot water boiler.
sorry for the misunderstanding.
charlie

[ToUtahNow]

Charlie,

I understood but you are also talking about turning on the power. Is your boiler controlled with a 24-Volt control system? What brand and model thermostat is it? When you turn your thermostat down does the termostat open? If you thermostat opens is there still power to the gas valve? Without this information and more it is hard to tell you what's wrong.

Mark

[subway41]

hi, Mark,
thanks for your reply.
the thermostats that we use are the basic type.
up to this year we have had no problems. we niticed last week that the heater was continually running even with the thermostat turned off. we changed the thermostat but it still kept running. on the boiler is a fuse and a power switch which shuts off the electric power to the control box.

[BILLG]

Sometimes old thermostat wires short. Disconnect them from the control and if it stops it's the wire, if not, most likely the control.

[plumber]

I am not sure what you mean by basic type. The brand and model number is really needed here.

From what I have read so far, my hunch is the limit switch should be replaced. But thats a pig in a poke since we are not sure what we have.

If you let the water heat up, then turn the unit off does it fire up immediately when you plug it right back in or does it wait until there is demand?

Does the boiler have an integrated electronic flue damper?

[plumber]

Subway41,

No offense but I really need to ask this other question. In your first post you had written "once we turn on the system". Who is "we", and does "we" have any experience at all working on or installing commercial boiler type water heaters?

I have a very scary mental picture of what might be going on in that mechanical room and really hope it is not an accurate one.

[subway41]

thanks everyone for your advise.
it turns out that the thermostats were fine, but there was a short in the wire from the heater to the thermostat.
great forum.
charlie