Heatmaker problem strikes again!

Ken C.

Today, I was called to service a Heatmaker HW-M2 (Mark 2) that was heating domestic water adequately, but heating the house poorly. Just a few weeks ago, I had another Heatmaker with the exact same problem.

In both cases, the low limit would not turn on the external circulator (for space heating). Replacing the low limit (which the homeowner did before calling our company) did not fix the problem.

I asked about this problem on the Wall last time, and was told that the low limit, which is an aquastat strapped on to the domestic hot water pipe where it exits the storage tank, has to reach approximately 160 degrees before it will activate the outside circulator. I was told that this is to ensure that there is adequate domestic water before the system focuses on space heating.

So, the un-answered question is, why isn't the pipe getting hot enough to satisfy the low-limit aquastat? I tried to call Teledyne-Laars tech support, but was on hold forever. Then, I thought about it: both homes are in the same city, which is known for poor-quality water. I also remembered reading that the heat exchanger coils on some Heatmakers need to be cleaned out (although neither unit was making a "kettling" sound). So, my theory (educated guess) is that the lousy city water created mineral deposit buildup on the heat exchanger coils, thereby preventing the domestic water outlet temp from reaching 160. Both units were about 10 years old.

First, is that theory correct, and is there any way to verify it without tearing the boiler apart?

Second, I don't understand how the domestic water outlet can reach 160 if no one is running hot water. Suppose no one has run the hot water for several hours, and then all of a sudden, someone turns the thermostat up. How does that low limit aquastat reach a hot enough temp to turn on the external circulator?

Third, how big of a job is it to clean a Heatmaker coil? Is it even worth doing on a unit 10 years old and trouble-prone?

Fourth, are the new generation Heatmakers (I believe it is the Laars EBP series?) less prone to mineral buildup on the heat exchanger coil?

I'm probably going to run into this problem again, and next time, I'd like to give a definite answer and good advice to the customer.

steve gates

you could be right on. Think of all that scale as a little blanket on the inside of the pipe.

As far as verifing try checking the temp. diff. between dhw in and out this should tell that story. Sorry I don't recall the # it should be.

It's kinda like a conductive thing. Keep the stat covered with insulation.

It's easier to change a coil than clean one. If cleaning I use CLR first. Put in some tees and valves and pump it. The new units have a flat plate in them. Yes they will plug up. With proper service they should stay clean. Depending on the water is how often you'll schedule cleaning.A softner is a big plus.

Sorry about tec support, I called twice last week and they were wrong both times.

Ken C.

Tech support

You said you called Laars' tech support twice and they were wrong both times. Can you elaborate?

Tony_8

Coil cleaning

First of all, the build up is on the INSIDE, not the outside of the coil.
Second, changing that coil may not be an option now that Laars has bought them out. Use Hydrochloric acid and a hand pump with the other side of the coil going to drain, to clean it best and quickest. If your not comfortable doing this, defer the call to someone with more experience.
Third, the LL will get hot by gravity from the tank when DHW is not being used.
Fourth, there is no kettling sound from the DHW coil because there is NO DIRECT FLAME ON IT. Kettling occurs when the combustion coil gets coated on the inside.
Fifth, on a call for heat the boiler fires. The LL only keeps the external circ from running until it gets to temp in the tank.
Sixth, EBP boilers use a plate heat exchanger for DHW. I think maybe they won't build up as quickly by design, but time will tell

Skippy

I have been reading on the wall for a long time but never respond to any of the posts for several reasons, the largest is that I have a reading and spelling problem. But on this on iteam I think that i may be able to help. First thing first if you call the Lars teck line never call the west coast line no one has that much time to waste. Second I spoke with one of the old tecks and his recomdations was to cut in tees and valves and run white vinager through the exchange with a pump for a half hour and that this would remove the build up. If you do go with an acid that is stronger FLUSH the system and newtrlize it. I have done the vinager several times on different and have been pleased with the results.

steve gates

Well I want to be nice so I'll say it wasn't inregards to a h/m.

Also the white vinegar will work o.k. if it ain't plugged to bad. No matter what you use rinse real well.

Ken C.

Tony,

Thanks for your reply (I think you were the same person who also replied to my post a few weeks ago). I'm getting a better understanding how these boilers work.

So, to clarify, is it possible that there could be enough of a deposit buildup inside the coil that the storage tank could NEVER get hot enough to satisfy the low limit?

And do you think that's what's happening in both of my cases?

Tony_8

'Twas I

Before also.

What happens is, the coil gets coated on the inside insulating the outside of the tubing from the heat it needs to feel. That makes it slow to react.

Heatmaker tried an internal sensor once, but it made the problem worse by restricting the flow and giving the minerals another place to "stick".