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Aquastat Setting

Hi, I have a Burnham V8 boiler with tankless DHW. I have had several issues over the last year or so with water temperature fluctuation and have had the boiler man out a few times. They replaced the Aquastat (a Honeywell L4006a) and put in a new mixing valve. First I had no hot water. They came back and then I had 185 degree water from the faucet. They came back and rectified that problem but it seems they partially closed the water feed valve so hot water pressure died anytime multiple faucets were used. 

I opened that valve back up. So now I have 115-120 degree water and good pressure. But the last remaining issue is fluctuation. Five minutes in the shower the water goes cold for a minute and then comes back nice and hot. I think it is the differential setting on the aquastat. It is set to 5 degrees with the hi set to 175 degrees. Is the 5° differential setting causing my hot water to short cycle? Should it be more like 20°? And if I change the 20° do I need to lower the maximum temperature by 10 degrees or so? I’m not concerned with efficiency or saving some money. I just want a good shower!

Last detail, my auto feeder sounds labored and I think it keeps timing out the feed cycle and shutting the boiler down due to low water. I have been manually filling it and will clean the strainer today. I figured I’d mention it but I doubt it has anything to do with the problem. I made sure the boiler had water when the fluctuation condition existed. 

Thanks in advance for any help!

Comments

  • Intplm.
    Intplm. Member Posts: 1,945
    Your new mixing valve may have burned out. The way your water temp. is fluctuating is a telltale sign that that is what is happening. Your temperature should come out of your faucets at 120 deg. You really should have NO temp. fluctuation as described.
  • AlpinaB7
    AlpinaB7 Member Posts: 11
    I will check and make sure that the water entering the valve is actually hot when the temp dips in the shower and report back here. The Watts 70a is just a few weeks old but I know that is no guarantee that it’s not the problem.
  • neilc
    neilc Member Posts: 2,703
    maybe post a picture showing how it's piped, including back to the boiler or tank
    known to beat dead horses
  • AlpinaB7
    AlpinaB7 Member Posts: 11
    edited February 2021
    Vertical pipes left to right
    cold in
    hot out
    mixed to sinks/showers
    cold from meter


  • Intplm.
    Intplm. Member Posts: 1,945
    That watts tempering valve is the problem.
    The problem that you are having with the water fluctuation is typical of that valve, watts 70a.
    What you need, to have proper hot water temperatures is a "thermostatic mixing valve."
    What you have currently installed is a tempering valve that tends to go bad often. It is obsolete technology for what you are using it for.
    Get rid of this valve. Change it to a watts thermostatic mixing valve. Model mmv-us-m1, or equivalent. For 1/2 inch diameter copper tubing.
    If you don't change it to a thermostatic mixing valve you will continue to have the temperatures in your hot water fluctuate.
    SuperTech
  • AlpinaB7
    AlpinaB7 Member Posts: 11
    I’ll throw one in. Looks easy to do. Is Watts the brand or are there others that are better? The more I read about the 70a the more I see people saying they are terrible.
  • AlpinaB7
    AlpinaB7 Member Posts: 11
    So it’s not the tempering valve. The tempering valve is being fed cold water when the shower temperature drops so there is no way it could provide hot water. 

    When I run the hot water continuously it comes out hot until the boiler shuts off—about 5 minutes. Then the water temperature drops until it is coming out of the faucet cold (this was tested in the 120 year old basement utility sink with separate hot and cold valves). Then the boiler kicks on again and after about 30 seconds the water is hot again. Then it keeps repeating. I confirmed this because when the water temperature at the sink drops I put my hand on the water pipe coming out of the boiler. It is cold. Once the boiler kicks back on I can not hold my hand on that same pipe.

    Any more thoughts on the 5 degree differential?
  • bburd
    bburd Member Posts: 912
    edited February 2021
    Widening the differential will make the problem worse. The aquastat is not sensing the drop in boiler water temperature quickly enough to maintain a reasonably stable temperature.

    Did the technician fill the aquastat’s thermowell with heat conducting compound when they installed the aquastat? If not, that should be done.

    Bburd
  • AlpinaB7
    AlpinaB7 Member Posts: 11
    I cant tell and don’t know if he did. Is it easy enough to remove the aqua stat to see? And your theory is correct because even when I had my hand on the boiler outlet pipe that was cold I was thinking why hasn’t this kicked on yet? It was slow to react.
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,517
    @AlpinaB7

    Take the cover off the aquastat and make sure the bulb is pushed all the way into the well. Your supposed to install heat transfer paste on the bulb prior to inserting it some techs don't use it.

    Leave the differential at 5 degrees making it wider will make the situation worse.

    You could boost the boiler temp but 175 should be plenty hot.

    Tankless heaters are not great a low flow shower head may help

    It's possible the tankless coil has sludge in it.

    Also with a steam boiler make sur the water level is half way up the water must cover the tankless coil
  • AlpinaB7
    AlpinaB7 Member Posts: 11
    I will do all that. The water level is low. I just cleaned the filter in the auto filler but it doesn’t seem to be filling it enough in the sight glass.
  • bburd
    bburd Member Posts: 912
    The water level should be at least halfway up the sight glass, that is. It should completely cover the tankless coil.

    Bburd
  • AlpinaB7
    AlpinaB7 Member Posts: 11
    No paste on the aquastat. But it’s in all the way. I’ll grab some paste. No water in the glass. I just filled it to half way 2 days ago. Not sure what’s up with that. No leaks as far as I can see. The VXT feeder comes on from time to time but it’s obviously not keeping it full enough.
  • neilc
    neilc Member Posts: 2,703
    boiler or steam system is leaking,
    now you need to find that leak,
    wet returns under slab?
    known to beat dead horses
    HVACNUTSuperTech
  • HVACNUT
    HVACNUT Member Posts: 5,831
    If you just fed the boiler and now there's no water in the glass, and running out of DHW, you've got a leaker.
    Is that a Hartford loop? Doesn't look like it from that angle. It might be leaking backwards right out of the return .
  • AlpinaB7
    AlpinaB7 Member Posts: 11
    No leaks are apparent. I don’t see water anywhere. No slab, it’s a basement. Something internal?
  • neilc
    neilc Member Posts: 2,703
    is there steam puffing out your chimney?
    known to beat dead horses
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,517
    @AlpinaB7

    Doesn't sound good when a boiler is loosing water and there is none to be found. When you get a warmer day shut the boiler down. When it is luke warm fill it up...over fill it until the steam supply pipe gets cold then shut it off and let it sit for an hour or so look for leaks. And while it's running check for steam coming out of the chimney as @neilc mentioned
  • AlpinaB7
    AlpinaB7 Member Posts: 11
    I had the boiler technician here today. He took off the stack and there are several holes in the boiler. Time for a new one.

    The auto fill put in 24 gallons in the last 24 hours.

    I have a gas meter bar in the basement. I’m not sure if the line is active from the street. Does anybody have any thoughts on gas versus oil? Any recommendations on a new boiler that has a similar configuration to the pipes so they don’t have to re-pipe everything?
  • SuperTech
    SuperTech Member Posts: 2,159
    Best recommendation that I can make is don't install another Burnham. The V7 and V8 series are known for premature failures.  The Burnham Megasteam seems to be much better quality than the rest of the cast iron boilers they offer. 
    Gas or oil depends on rates in your area. Regardless of fuel choice or brand of boiler the installation is the most important thing. Make sure that the installing contractor is familiar with steam heating and follows the installation instructions specified by the manufacturer.  We see an awful lot of boilers on here that are installed incorrectly. 
  • AlpinaB7
    AlpinaB7 Member Posts: 11
    Looks like I’m getting an oil Burnham Megasteam. It is available locally and can be installed tomorrow. The old one will never make it long enough to put in a gas line.