Hot coming out of cold... Boilermate/Coil issue?

[watson524]

Hi everyone,

When we first built our house in 2002, we had just a Weil McLain Oil Fired Water boil using the coil for potable hot water and feeding our hot water baseboard heat. In January 2006, we added an Amtrol Boilermate. Our oil company did the install for us and I thought when we talked about it, they said potable hot water would just come from the boilermate and the coil would go away.... Over the years, we've had to turn down the boilermate because the hot water was so hot (we have it set around 130 now). In the past few years we've noticed that sometimes when we turn faucets on (doesn't matter if single lever in say the kitchen sink or dual lever in a bathroom) it'll be cold, then run warm/hot for a while then go back to cold. Also, our hot at full faucet strength is REALLY hot, like steaming....

Ok fast forward to last week where our one toilet was running. I figured ok, time to replace the flapper, no big deal. Stuck my hand in the tank and the water was very warm... What the heck. So I turned on that bathroom fauct, HOT water coming out of cold..... So we start digging, no mixing valves under the sinks, figured it'd be odd for all cartridges in the faucet handles to be on the fritz so we called a friend who knows more about this stuff than we do.

He went and looked at our boiler and said "why are you still using the coil?" Huh... dunno... that's what the oil company did, thought it was supposed to be taken out, that's been like that since 2006 with Amtrol Boilermate install. He said he would suspect that's causing the issue. The boiler is set at 160 low and 180 high. Water doesn't know what's calling for it, it just goes where there's no resistence. He said us turning down the boilermate to make it a better temp probably just exacerbated the fact that we're still using the coil for hot water and the boilermate is really just a big storage tank. Does that make sense? there's a mixing valve right above the coil that he didn't want to mess with not being an expert in these things but I told him I knew just the site where I could ask such things :-)

I have pictures I can post if need be but basically, cold goes in to coil and over to boilermate on the bottom there and also to house piping. Hot pipe comes out of coil, goes to house piping and to the top center of the boilermate, then from the boilermate there's 2 other pipes, one to circulating pump and one to flow check valve (and a blow off pipe off the boilermate too).

He said in his experience he would have expected to see the pipes to the coil cut off and left open (something about boiling steam out and going kaboom) and then the pipes from the top down to the coil cut and capped off.

He said maybe the installer thought that if the boilermate crapped out, we'd still have hot water but that he thought the boiler could be turned back to 140 - 160 too since it'd be used for just heat if piped the way he'd expect to see it and then basically, the boiler shouldn't really run at all in the summer when heat isn't being called for since the potable hot is coming from the boilermate.

We also ran a thermometer in various streams of hot water (kitchen and two bathrooms) and were at about 155 - 160 which he said is WAY too hot.

Does it sound like that's why we're getting hot from cold at times and that our piping in the basement is goofy?

thanks in advance! sorry for the long post, I just wanted to give as much info as possible. He also mentioned something about the boiler being able to do a cold start and then my eyes glazed over...

[jadnashua]

There should be a tempering valve on the outlet of the WH, and it may be on the fritz. that is what should moderate the water temp output from the WH to a safe level. Hard to say exactly what you have without being there or pictures. The logic board may need to be adjusted to tell the boiler not to maintain a certain temp to provide the water from the coil. Then, you could remove the inlet and outlets to it.

[watson524]

The only valves on it are down on the bottom with the spigot where the cold line is which i assume is to drain the boilermate if need be. Then on the other side there's a black dial where 120 degrees is marked between the 3 and 4 and we have it JUST BARELY above the 3 and given that the hot water at the tap runs about 160 degrees which is much closer to the boiler coil setting and the fact that hot from the coil is still piped in to the house lines and the boilermate, it looks like something goofy is going on. plus things don't fluctuate unless we actually go mess with a dial. i've attached some pictures to hopefully clarify what i'm trying to say and can definitely take more if need be. thanks!

[Tom Sawyer]

You need to get somebody to straighten the mess out. Cold water feeds the cold inlet on the boiler mate and the hot comes out the top. Two 3/4" tappings at the bottom are the boiler feed and return pipes. The old tankless coil should be either shut off or capped. The dual aquastat should have the low limit disabled

[watson524]

so my friend was right in that that coil connection should be gone. he said that the pipes into the coil should be cut JUST above that mixing valve and left open to air and then what comes down from the top should have caps put on them.

is that legitimately what is causing our hot water to be SO hot because we're really still using the coil? (and thus more oil than need be... gggrrr.....)?

and the aquastat, is that the gray box on the front that has a high and low? he did mention it's possible that control unit needed to be changed out but it wasn't his expertise so....

[watson524]

wait wait wait..... hot OUT of the boilermate DUH! (I just reread your post)..... well then here's more info... so we have a line out of the coil (that i have marked as hot in the picture)... that goes up and comes across and joins with the hot pipe going UP From the coil and into the hot water pipes for the house. so the valve right near the control box is open to send coil water up and the valve near the coil hot and boilermate top pipe come together is open so it's like it's drawing both at the same time. But again that may only answer why our water is so much hotter at the tap than we would expect but i don't get why the cold tap goes to warm/hot and then usually back to cold at various places.

also, if you were using the boiler for heat only, what would be the setting? my friend mentioned he thought 140 was the accepted level.

ADDED INFO AFTER "FIELD TEST". I turned the kitchen single lever sink handle to hot and left it run and went and watched in the basement. The circulating circuit on the argo panel for the boiler mate never came on. At 5 and 13 minutes, the well pump came on for about a minute. At 15 minutes the boiler kicked on because the low temp had dropped below the setting. The mixing valve thing between the hot and cold at the coil is all the way to the right (which I assume is closed. Not sure what any of this means.... but I wanted to report back.

[Tom Sawyer]

The boiler coil needs to be totally out of the loop, it causes a pressure and flow imbalance in the system and it's COSTING you money. The aquastat does not need to be replace, the low limit needs to be disconnected ( you need to find a service professional that knows what wire to remove and cap ) I would be really really pissed at whoever installed this thing because it appears that for the most part you have been continuing to use the tankless coil.

[watson524]

oh trust me, now that i know something about this... i am really really pissed. i just called and talked to the owner of the oil company and i was like "here's what i've found, all these years never thought it was related to this, blah blah blah" and he said no the coil should be out of it (but didn't think having it in it is causing ALL of what i see) but he said either thursday or friday (I'm not home tomorrow) he'll send someone up and to just call him tomorrow to confirm it's still ok to come one of those days.

so the burst of hot when turning on cold can be because of things "crossing" in the system. my friend said basically, water doesn't know where it's going or what's asking for it to go, it just goes where there's the least resistance. and so all this time the boiler has been firing more than it needs to i guess.

what should the high limit on the boiler get set to for JUST hot water baseboard heating? is 140'ish right?

[jadnashua]

140 on that style boiler is probably too low. The key thing is what the return water temp is, and if it gets below 130 or so, damage to the boiler can occur because of thermal shock and condensation. To keep the return from getting too low, you'll probably need 150-160 at least.

[Tom Sawyer]

180 is pretty much what most high limits are set at. If the house won't heat, bump it to 200

[watson524]

ok, for my own learning, can you explain about the thermal shock and condensation? this is cast iron on the inside (from what the trusty book tells me) so I wouldn't think condensation would matter but... i get the idea of hot to "cold" (if by cold we mean 130) cracking a "block" so maybe that's the issue. I was thinking since we aren't making DHW maybe we could turn it back some vs the 160 - 180 it's at now but it sounds like it should just stay with the high as is and then take the low out completely. We also have a heat pump on our central AC (which will likely lead you to the question of "then how come you have hot water baseboard?" yeah um... because when we built, I didn't think we needed central air but after 8 years of it, I bought a clue last summer) and a propane fireplace with fan that heats the downstairs pretty darn well.

[Tom Sawyer]

Since you are not making domestic hot water you can cold start the boiler. There is no need to maintain temperature. Look into a outdoor temperature re-set control also. It'll save you at least 10%

[watson524]

ok.... more questions if you don't mind. What is this cold start? My friend mentioned that too but it was in the midst of the "what the H%!! did they do THAT for?" so i sort of glazed over. i'm thinking it means that unless a heat zone is specifically calling for heat, it doesn't run to maintain the temperature? how insulated are these boilers? meaning, how far would the temp drop (unfinished subground basement so say 55'ish degrees minimum, warmer in the summer) and then have to go all the way back up to 180 or so since that's what the aquastat would set as high? i'm thinking it would run longer but less often which is probably good. but then do i need to be concerned with what jim said as far as too cold coming back into it?

and this outdoor temp re-set control... can you explain that more?

sorry to be a pain but apparently a homeowner needs to know darn near everything (at least in theory, i'm still trying to learn how to solder a nice line on a copper pipe LOL!) before inviting contractors into their house. which, please don't take offense to that statement since i KNOW there are great contractors out there and it's the smaller percentage that give folks a bad name.

[jadnashua]

When providing heat, if the return water is too cold over a long period, you can get condensation on the heat exchanger. This can cause it to rust out and can affect the flue as well. Modern high-efficiency boilers are designed for that and use corrosion resistant materials, older ones are not - they expect the return water to be hotter. How cold the heat exchanger is also affects the temperature of the flue gasses.

[Dana]

The flue gas temp is also an important factor- masonry flues & terra cotta flue liners can be damaged by prolonged cold operation of an oil boiler. At 140F return water you have some margin, but a stainless flue liner is still recommended. Cold starting on a hot-water heating burn with an indirect isn't too bad though, since the thermal mass of the indirect ensures a minimum length to the burn. Cold-starts on short-cycles (as can sometimes happen with low-mass emitters such as baseboard when heat loads are low) can result in condensation issues (boiler &/or flue.) Improperly set outdoor reset can also be a contributing factor.

In most pre-1980 homes (and many therefter) with baseboard the baseboard lenghts was designed for 180F operation at the 99th percentile coldest day of the year, but the heat loss was typically overestimated, and 160F works just fine, and usually results in about a 5% reduction in fuel use even without economizer or outdoor reset control. If the house has had insulation, window, or other weatherization upgrades since the original baseboard operation it's often the case that the heat could be delivered with 140F water, but that would guarantee that the return water to the in the condensing zone. In those cases outdoor reset is the wrong approach- outdoor reset only changes the high-limit, with some amount of hysteresis, and if the radiation can deliver design day heat at the boilers low-limit it's buying you exactly nothing (except higher risk of condensation problems.) Smart "learning" heat purging economizer controls such the Intellicon HW+ or Beckett Heat Manager programmed with 140F as the min return temp during burns better protects the boiler, but are able to draw the temp of the boiler down below 140F at the end of the burns, reducing standby losses substantially. These devices anticipate the end of the call for heat by sensing return water temp & it's rate of change "learning" from prior burns the appropriate time to turn off the burner while the circulator is still running and the room thermostat (or indirect aquasat) is still calling for heat, allowing the system temp to drop, "parking" the boiler at a lower temp. A boiler + distribution plumbing that ends it's burn at 180F when the room thermostat is satisfied has 2x the standby loss of a system that is heat-purged to 130F at the end of a cycle.