Running out of Hot Water

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Old 02-26-11, 09:59 AM
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Running out of Hot Water

Was hoping someone could shed some light on my situation.
We have an oil burning forced hot water furnace with 3 zones and tankless hot water system.
There is a small expansion tank above the furnace which i believe is just the supply line feeding the furnace.
There is a Honeywell thermostat on the front of the furnace and the settings are Low 140, High 180 and the Differential is set to 15.
The temperature gauge on the front of the furnace reads 190 degrees.
The water coming out of the faucet in the 2nd floor bathroom is close to scalding.
Unfortunately the mixing valve adjustment is stripped and needs to be replaced.

The main issue aside from the mixing valve, is that we run out of hot water pretty quickly in the 2nd floor bathrooms. It seems that if we turn the thermostat up for the 2nd floor area, that the hot water gets replenished. Kind of makes sense that by turning the furnace on, we are heating up the water passing through the heat exchanger again and therefor heating up the hot water.

Im not entirely sure how the hot water loop works. Being that its tankless, i understand i have a limited amount of hot water, so when it runs out the only way for the water to heat up again is for the furnace to run right? If all three zoned thermostats are satisfied, then the furnace wont run and then no hot water.

Do i have this right or can the Honeywell thermostat on the front of the furnace also control the hot water in some way?

This winter has been the first time that we have had this issue with running out of hot water. What could have changed?

I know installing a secondary heating tank will help, but why didnt we have this issue previously?
The copper pipes were all replaced about 4 years ago with that new plastic piping. Most of which is uninsulated. Still why no issues the past 3 winters?

Any help would be appreciated.
 
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Old 02-26-11, 10:19 AM
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can the Honeywell thermostat on the front of the furnace also control the hot water in some way?
That 'thermostat' is actually called an AQUAstat...

It is what is called a 'triple' (basically because it has three dials) aquastat. The LOW and the DIFF will run the boiler to keep it warm in the absence of a heat call. The HIGH setting establishes a HIGH limit that will only allow the boiler to hit that temp before the burners shut off... on a heat call only.

In the absence of a heat call, you should notice that the BURNER fires up occasionally to reheat the boiler water, and that it will also fire up when there is a demand for hot water, i.e. shower, clothes washer, etc...

Sure you will get hotter water when there is a heat call because the water in the boiler is hotter. You do need to get that mixing valve repaired... scalding is dangerous!

Those coils have a tendency to get 'limed up' over time... reducing their ability to provide enough hot water. The mineral in the water supply build up and reduce the capacity. That's probably what's going on...
 
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Old 02-26-11, 07:04 PM
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Lack of mixing valve also draws hot water faster, and leaves a lot stranded in the pipes, too.
 
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Old 02-27-11, 08:26 AM
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Thanks NJ Trooper,
I was just checking the hot water line going into the mixing valve and its cold to the touch at the moment. The 1st and 2nd floor temp is currently 68 degrees and the furnace just shut off.
There is thermostat wiring going up into the ceiling from the Aquastat along with the other zone thermostat wiring. Where would it be going if the Aquastat is only controlling hot water?
The furnace is about 25 years old and there is some lime build up around the copper fittings and brass nipples leading into the heat exchanger. Your probably right about the heat exchanger needing to be replaced.
Its a Well Mclain Heater Model E-624 and it looks like its still available for purchase.

Edit: The cold pipe question was probably a dumb one. I left the hot water running at the kitchen sink and then went down stairs and grabbed the pipe. It felt hot this time. Well looked at things a little closer and traced some of the wiring and flex conduit around. Looks like one of the heating zones is wired into the Aquastat, so im sure thats where the 3rd thermostat wiring is from.

Another question the mixing valve has a brass hex shape nut on the top of it that appears to be threaded into the valve. Is it possible to get kits to rebuild these valves? It has the following info on the side of it. Beacon Mixer 69. The nut has the following temps stamped into it. 120, 140, 160 and 180. Does the screw only have to be turned a 1/4 turn to set it at these temps?
 

Last edited by LOTL2; 02-27-11 at 09:11 AM.
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Old 02-27-11, 05:16 PM
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Is it possible to get kits to rebuild these valves? It has the following info on the side of it. Beacon Mixer 69.
That company is apparently gone out of business... I would plan on replacing with one of the major brands... Taco, Honeywell, etc... you may have to do some minor repiping cuz that one you have is different configuration than the new ones. And, it might just be part of the problem with the hot water too.

Your probably right about the heat exchanger needing to be replaced.
There is a procedure that can be performed by a pro with the equipment where an acid solution is pumped through the coil to remove the deposits. Sometimes it works, sometimes it doesn't. Sometimes it causes more problems than you started with! (pinholes in the copper tubing).

It might cost a couple hun to get a guy in to do that... and he will probably have to cut into the piping to add the valves that he needs to pump the solution... so if you are going to replace the mixing valve, that would be the time to do it.

It's EASILY gonna cost at LEAST $300 to replace the coil, and there are problems that go with that also. If the bolts that hold it in are rusted, and any of them break while trying to remove, count on the cost going up because they will have to drill and tap new bolts.

I think I might try replacing the mixing valve first, then go from there. No matter what course you take after that, you will at least be able to reuse the new valve.

Do you have the room for a tank? Going to an indirect fired water heater is by far the best choice... count on at least $1000 installed.
 
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Old 03-02-11, 03:40 AM
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Thanks again ill start with a new mixing valve and go from there.
 
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Old 03-02-11, 05:24 AM
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Wouldn't it be advised to turn the low limit up to 160 as well? If the thermostat is calling for heat he states his hot water supply is better and all that is doing is raising the water temp. With a busted mixing valve and a lot of hot water going through the tankless I would think that extra 20 degrees would help a lot.

Just the ramblings of a newbie
 
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Old 03-02-11, 03:41 PM
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Turning up to 160 is that much more of a risk of scalding since the mixing valve is not working properly. Water that hot has the potential to cause serious burns in like 1 second.

It will also burn that much more fuel keeping the boiler that much hotter 24/7.

Fix the mix first... gotta have all the ducks in a row. We wouldn't drive our car to the shop for a tune up if it had a flat tire, right?
 
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Old 03-02-11, 04:21 PM
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Originally Posted by NJ Trooper View Post
Turning up to 160 is that much more of a risk of scalding since the mixing valve is not working properly. Water that hot has the potential to cause serious burns in like 1 second.

It will also burn that much more fuel keeping the boiler that much hotter 24/7.

Fix the mix first... gotta have all the ducks in a row. We wouldn't drive our car to the shop for a tune up if it had a flat tire, right?

Certainly makes sense!!
 
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