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Thread: mixing valve issues

  1. #1
    builder, designer varmint's Avatar
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    Default mixing valve issues

    Hi: this is my first post here! I have a Honeywell AM-1 mixing valve (Sparco) installed on my boiler's hot water coil- it's a steam heat boiler, so the coil water gets too hot for comfort or safety, and it's worked fine for 3-4 years. Lately, the hot water pressure seems to pulse up and down, regularly, maybe 3 times in 2 seconds or so- but not all the time. Happens at any hot water supply, while the cold flow stays constant. This is at a fairly low flow rate (we're on a low yield well, so nothing uses more than 1 gal. a minute) and it doesn't cause a problem, just an annoyance. I guess it gives the shower pressure balancing valve some exercise? Before I look for a new element, I thought I'd ask if anyone has any idea about this? Thanks!

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    What do the instructions say, if anything, about deliming the coils in the boiler? The passages could be getting restricted because of mineral deposits.

    Is your storage tank in good shape? Does the pump and overall system pressure fluctuate?
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
    builder, designer varmint's Avatar
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    No de-lime or anything else... I have no instructions. Until recently, our water was acidic, so mineral build up was non-existant. The pump pressure and cold water supply are smooth, this problem is only with the hot water, and not all the time! Sometimes, flow is smooth, sometimes pulsing. Always at a modest flow rate... 1/2 gallon a minute or so. Once I switch over to the summer demand heater, I fully expect the problem to disappear, and then I will tear the mixer apart to see what I can clean/fix. There is no storage tank in the system, other than the well pressure tank.

  4. #4
    builder, designer varmint's Avatar
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    Well, there doesn't seem to be that much interest in this topic, but FWIW, I have decided that the mixing valve is "hunting" because of pressure differences between the hot and cold water supplies- the flow rate thru the coil is reduced, so the cold pressure is greater. As I go to less cold mixing input- hotter output, the pulsing is reduced. I will try acid flushing of the coil, when I shut the boiler down for the summer, but I am not all that hopeful.

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