I bought a house last year that has a Weil-McLain boiler/tankless
heater. I believe it was installed in 1992. It looks pretty beat
up---more rust and the like than I would expect on a boiler that's
about 15 years old---but I'm told that the water around here is pretty
hard and that it eats up boiler. (On the other hand, I have a water
softener system, so what's that all about?)
Anyway, the boiler simply doesn't provide enough hot water. We can't
fill up the bathtub, and showers get cool after a short period of
time. Even when the boiler kicks back on, the water only becomes
warm, not hot. I can deal with this in the shower, but I'm concerned
about the washing machine and dishwasher.
The heater part of the boiler has three controls as far as I can
tell. There are two thermostat controls that determine when the
boiler fires on and off, and a valve that blends the hot water from
the heater with cold water to deliver to hot water faucets.
If I want more hot water, how should I adjust these things to serve us
Also, I read on the Weil-McLain web site about an indirect-fired water
heater. Is this something that adds onto a tankless system to provide
extra hot water? (I have no idea if this could physically fit into
our mechanicals closet, but it's somethng to look at if it would take
care of the problem we are having.)
Any suggestions appreciated!
Find the operating manual (it should be kept near the appliance or download
from Weil-McLain's website) and read the troubleshooting section. It's short
and to the point. It looks and sounds to me like you need to call a pro to
service the appliance.
First, Don't touch the setings for the hi and low limit. They are the
dials on the primary controller. Typically it's a Honeywell. The
settings(typically) should be around 180 for the hi and 160 for the
low. Leave the other dial for the differential at 20. Lets start
Okay, now to fill a bath tube with water is going to use up a lot of
hot water. The typical tankless is about five gallons. YOur boiler
should be firing during this time. It may cycle a few times, but for
the most part it should be firing. Anyways, since you mentioned hard
water you may have two problems. The tankless coils could be caked
with scale and or the mixing valve could be fried. Have you tried to
incease the level of hot water? If the dial is maxed out then you may
want to start with this. Do you have any plumbing skills? Start with
the smaller and cheaper parts before doing anything to the boiler. I'd
replace the mixing value first.
You mentioned indirect hot water. This is your next option. I say
this because replcing the tankless is almost next to impossible. Most
of the time the a stud or several tend to break cause more of a
problem. If the tankless is not leaking I'd leave it be. You can add
a booster/holding tank onto the tankless. Let the tankless heat the
water and store it in a 40 or 50 gallon tnak. The indirect is tied
into the boiler as another zone and will require additional
electronics to turn on the circulator for heating the water.
Another good site to check is heatinghelp.com. Lots of resources
On Wed, 20 Jun 2007 12:40:34 -0700, Paul Flansburg
I'd agree with the above except that a tankless coil CAN be replaced.
Many boilers about the age of your Weil-McClain and newer have used
stainless bolts to fasten the tankless coil. In any event, with some
caution, time and penetrating oil, I've removed tankless coils. A
replacement coil is only about $150 plus labor if you don't do it
The tankless coil is simply a copper coil submerged into the boiler
water. Typical output flows from a tankless coil is about 2.5 to 5
Gallons Per Minute. That's up to 5 GPM of VERY hot water. Thus the
mixing or tempering valve is often used to reduce the likelihood of
Another treatment for a "limed up" tankless coil is to flow
hydrochloric acid through it. I've done it myself and fumed up the
basement quite a bit so it has to be done with plenty of ventilation
and extremem caution, with protective rubber gloves, etc. It was quite
successful and restored the hot water output flowly to normal. Most of
the younger techs in the HVAC world won't do the acid cleaning. Most
old timers will.
An indirect water heater is an option. As the poster above states, it
runs as a seperate "zone" off of the boiler. However, such an
installation is fairly expensive and will consume a good amount of
space in your utility room. An indirect water heater will take up
nearly as much space as your boiler.
Here's a picture from the inspectors report that shows the boiler.
You can see that there's a lot of rust at the bolts that hold the coil
in place. One of the oil company service people said that we could
try to replace the coil, but the risk is that we'd have to end up
replacing the whole boiler if things go bad...
That rust is from water leakage. It looks like the tankless coil
gasket might already be leaking. It should be fixed one way or
Obvously, I can't tell you what to do but I'd have a crack at
replacing that coil while the weather is still warm.
Try loosening a bolt or two. If bolts snap, they can then be drilled
out, the holes can be retapped and things should go well.
Auto mechanics drill and rethread cast iron for helicoils to repair
stripped spark plug holes. This operation is no different.
What's the worse case? Replacing the boiler?
That will cost you about $2000 to $4000.
Installing an indirect water heater will likely cost you a good $2000.
I find that HVAC pros won't do jobs like this because they don't want
the risk and don't want to spend the time when easier dollars can be
made elsewhere. The fact they don't want to do it doesn't mean that it
can't be done. None of them will attempt acid cleaning of the coil?
Or leave it as is and install an electric water heater as another
poster suggested. It will work fine but your electric bill will
skyrocket. With the limited space that you have, your options are also
If you didn't always have the water softener, deposits can be lining the
inside of the domestic coil, insulating it from the hot water around it. As
the others have said, do the simple things first, and if they don't solve
the problem, definitely go with an indirect. It will need to be connected as
a separate zone, with a relay if you have separate circulators, or by way of
an additional zone valve, if that's how the system is set up, in any event
you will have plenty of hot water
Maybe not what you and the others want to hear, but years ago, when my
kids were in their teens, it became impossible to meet all of the
shower, bath, laundry demands. I simply installed an electric hot
water heater in series with tankless coil output. The boiler then
preheated the water and the HWH kept it hot. Thru a set of
judiciously placed valves I can cut the HWH system out of the system
(In hurricane aftermath, the generator will handle the boiler, but not
My Burnham is 40+ years old; no way would I ever attempt to replace
that coil - nor would my HVAC guy.
Works for me
I have the same setup you have. Weil-McClain tankless oil
boiler...their smallest one too. It was installed in 1999 and has had
no issues since. I believe my hot water supply is endless. We have
used to for filling large bathtubs, running dishwasher laundry often
at the same time. Our issue has been a notice in pressure drop more
than anything else. Our water though is always very very hot and we
have never run out. Boiler is set at 180F high and 160F low. Our
water is not hard at all, all have is a whole house filter. It's
either you mixing valve or your coil...or the aquastadt. These units
are generally very reliable.
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