AO Smith modulation valve?

Larry_7

Re-lit pilots at a rental house today. Older boiler (blue/white cabinet). The burner never came off low fire. The modulating valve was non-functional. 100 MBH boiler firing at 35 MBH. We won't be servicing the unit but just curious. Is it worthwhile to replace the valve (assuming it's available)? Never seen one do this before. Could the valve be abandoned and use a step-open main valve? I feel that either way, the labor and material cost would make a new boiler more sensible, especially since the thing was installed in tight quarters with the control side facing the wall.

Thanks,

Larry

Unknown

Larry, what kind of valve is it?

if it is truly a modulating valve system a step open can not really be used. Need a little more info to give you an answer.

By the way I have not forgotten about you. I have the valve and I am doing some research with White Rodgers and also Carrier. I also had someone else with a similar problem on a different unit with that same WR valve. I will let you know what I find out.

Larry_7

Timmie

The valve is downstream of the main valve just prior to entering the cabinet. My understanding is that it allows rated input maybe 5-10 seconds after ignition. It has an adjustable knob. I'm not sure about its function. I've always assumed it controlled when and/or how fully to allow main gas to the burner. It also has a capillary tube that runs into the cabinet. All the old copper coil Smiths had one I think...even back as far as the old Ber-Kays. I was told early in my carrer just to "not mess with that thing" and have obeyed faithfully ever since. Now after seeing one not work, (I think), I want to know more. Not messing with stuff (within reason) guarantees continued ignorance.

Thanks,

Larry

PS
As far as the W/R valve, I'm glad to hear (in a twisted kind of way) someone besides me may be seeing the same problem.

Unknown

Is this a Honeywell V-5155

Thermostatic Valve? It is found on page 48 of the 2002 eighth edition of Honeywell Catalog. This valve modulates per setting relative to sensed temperature. It is still available. Those valve can be calibrated by the way. It must be calibrated to a measured temperature. If it will not adjust temperature relative to flame size then it has lost its charge and has to be replaced.

Larry_7

Don't know

I don't have the catalog but sounds like you and me are talking about the same part. I've always observed the burner come on low, then ramp up. Never seen one modulate back down although sounds like it may do that too. So many questions, so little time.

Larry

Unknown

Yes they will modulate

back down as the temperature goes up and there is still a demand for heat. That is the economy of the unit.