DHW problem, tankless boiler, Weil McLain


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Old 02-05-23, 08:51 AM
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DHW problem, tankless boiler, Weil McLain

I have the proper temp (very hot) water up to the mixing valve, but I get a mix of slightly warm to hot coming out of the faucets! Never know what I'm gonna get! I have good water flow & pressure, & have replaced the mixing valve innards, but still have the problem! I also pulled & checked the aquastat probe & set the boiler temp higher & nothing seems to help! When I had a problem in the past, I would flush the coil and/or replace the valve guts & that would solve the problem! I also have cold well water, if that means anything!
Thanx!
 
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Old 02-05-23, 10:54 AM
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MP,

The first thing to do is get the boiler up to temp. then turn on your tub because that is the biggest draw and with the water on, feel the pipe from the tankless before the mixing valve to see if the temp of the pipe gets cooler. This will tell you if it's the coil or the mixing valve.

The coil over time gets limed up which acts as insolation and doesn't permit the fresh water to absorb the heat from the boiler as the fresh water goes through the coil.

The average house pressure produces about 7gpm of running water but your tankless coil is between 3 & 4 gpm which means your water is coming in faster than your coil can heat it, even if the coil is new, let alone once it gets limed up. They make a pressure reducing valve for tankless coils to match what the coil can put out which saves water and helps prolong the life of the coil by cutting back on the excessive wasted water going through it.

If during the test the boiler comes back on and the pipe is still scalding hot the problem is most likely in your mixing valve. If the pipe cools down after the coil and before the mixing valve then no matter how high you turn the boiler up you will still run out once the fresh water starts moving through the coil.

Hope this helps a little.
 
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Old 02-05-23, 01:54 PM
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Thanks for the tip! Actually the water does get hotter after running for a while and today when the "other half" was showering, the water did stay very hot up to the valve and there was a cooling period in the shower after starting & when it got hot again! Does that make sense? I installed a repair kit in Dec. '22, but that didn't work! I have a GO5 in my little shack so I wouldn't think there would be a heating problem! I've had nothing but trouble with this unit! I'm going to flush the coil anyway, but I have to put in a couple of gate valves first because I have one of those circulators in the line and when I tried before I couldn't get the pump to prime!
Whew! Thanx!
 
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Old 02-05-23, 03:16 PM
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Yes, that makes sense. If the shower starts when the boiler is off on Hi-limit the water will get cooler @ the shower until the boiler comes back on to reheat the boiler water. If the coil was clean you wouldn't notice it but limed up, the coil needs extremely hot boiler water to heat the water in the coil. It looks like they are up to 5gpm for new coils.

When cleaning the coil it is done from the inside with acid or it won't work.

590-921-612 - Weil-McLain 590-921-612 - Tankless Heater for Weil McLain WTGO-3, WTGO-4, WTGO-5, and WTGO-6 Boilers (supplyhouse.com)

SupplyHouse.com - Plumbing, Heating & HVAC Supplies - SupplyHouse.com
 
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Old 02-06-23, 01:27 PM
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Yeah, I use a little pump & vinegar for the coil if I have a problem! I checked as you suggested & the water is scalding to the mixing valve & barely warm after! I disconnected the circulator too & no difference! I just replaced the innards of the valve in Dec. so maybe I have the wrong repair kit!
 
  #6  
Old 02-06-23, 01:47 PM
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Sounds like it might be the mixing valve in your case. What brand of MV do you have. As far as vinegar goes, I never tried that. We always used acid. If you want to try something, remove your MV guts and run straight hot and check the results. The water will come out at the samed temp as the boiler so be very careful. You can lower the boiler temp down a little and mix the water at the fixtures until you get the right parts.
 
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Old 02-07-23, 11:31 AM
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I'm thinking the problem may be the check valves! The hot water pressure is a little lower, possibly due to "coil crud" and the cold water is partially closing the hot water check valve! I'm going to flush the coil and if that doesn't do it, pull the check valve! Who's gonna know?
I use 5% vinegar for the coil to save the pump! Mine still fell apart the other day anyway 'cause I guess I didn't flush it good enough! All the vanes fell off the gear & the metal front plate is all eaten up!
 
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Old 02-07-23, 12:02 PM
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Is it possible to post pics. I'm confused. What check valves and pump. I thought you had a tankless coil so what check valves and pump are used with that.
 
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Old 02-07-23, 09:33 PM
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Hybrid DHW boiler tankless coil & water Heater

Tankless coils systems have many issues.

DH ended inadequate shower water problem going to “hybrid” system, adding separate water heater with 50 gallon tank( whether fire directly (oil, gas or electric). Original 50 gallon oil water heater, was replaced after 20 years, with $500 gas https://drive.google.com/file/d/1Doc...ew?usp=drivesd

In hybrid, cold water source is fed to water heater tank inlet through a check valve along with hot water circulated by Taco 007 pump from tankless coil.

On tanks outletis a tee. One side of tee supplies hot water for safety. though tempering valve to showers. Other side of tee return to water tankless coil.

Hybrid expands boiler tankless coil DHW capacity in winter and is lower cost that direct heated tank, In summer turn off boiler and turn on water tank’s heater.

Tank temperature aquastat is controlled to 1 degree with $20 eBay unit. Probe is placed under insulation at tank valve.

https://www.ebay.com/itm/26371152402...taWPHl&LH_FR=1
 
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Old 02-08-23, 06:56 AM
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I have a Honeywell AM 1 series MV. Some or most valves now have check valves in them because some locales require them for whatever reason! They're supposed to keep the hot from going into the cold line & vice versa!
The pump I'm talking about is the water transfer pump I use to flush the coil!
 
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Old 02-16-23, 07:34 AM
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Your boiler might need to have at least one heating zone calling for heat in order to churn the water inside the boiler and improve the heating of a tankless domestic hot water coil that is handicapped by lime deposits.

Some FHW systems have a separate zone for domestic water taking the form of a pipe from the supply manifold going to a circulator pump and straight back to the return manifold. This runs the domestic hot water zone without sending any FHW to any radiators.

"" I also have cold well water, if that means anything! ""

You can construct a preheater for domestic hot water using several yards of finned pipe dissected from baseboard FHW radiators. Mount this at least an inch away from the basement ceiling or wall and not in the way of persons walking by.
 

Last edited by AllanJ; 02-16-23 at 07:51 AM.
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Old 02-19-23, 08:27 AM
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Hi, all!
Everything seems to be working well now! There was a lot of "stuff" in the coil! Flushed until the copper color was coming out & now it seems to be ok!
Thanx!
 
  #13  
Old 02-19-23, 08:00 PM
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A contributor to problems in hot water system are rust particles from city water mains. On valve seats cause leaks, in coils and tanks partially block or debri promotes failure.

A “preventive maintenance” solution is $37 water filter on feed to both boiler and DHW system to reduces many problems.

Filters with clear plastic housings are best. Some have built in valve for shut off when changing filter. There are many types, this is low cost.

DH filter has never clogged, but change $20 element annually. When new element is install, it soon appears rust colored. In 50 years have not had tankless coil problem, even with low, 60 psi city water.

https://www.amazon.com/Pentek-10-Sta...k-10-Standard-


 
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Old 02-20-23, 02:02 PM
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I have hard well water! I do have whole house filters, but they pretty much just filter out sediment on my arsenic remediation set up!
 
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Old 02-20-23, 08:12 PM
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Homes use many types of filters for various issues. Post 13 filter is only for heating and DHS, relatively low volume so only is change annually.

DH home uses another whole house filter for cold water feeding faucets, showers, etc. Lawn sprinkler system has separate unfiltered connection to water meter.
 
 

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