Gas Boiler Staying Hot

BillyNYC

Hi, I Have a Hydrotherm Gas boiler used for heating only to my parents home. There are 3 zones, 3 circulator pumps, 3 zone relays and 3 thermostats one to each zone. The boiler is original (1975) and works to heat the house. I have noticed one issue though. It stays warm as per the aquastat settings even without a call for heat and/or the thermostats set at off. The aqua stat is set to 190 with a 20 degree differential. Even without a call for heat, it fires and keeps the temperature as per aqua stat. Isn't this very ineficient? Its a baseboard system. While staying hot, the circulator pumps are NOT working or circulating the water. It just keeps the water in the boiler hot.Thanks in advance

JUGHNE

Does it heat domestic water also....for faucet and showers etc.?

BillyNYC

no, just Heat

BillyNYC

aquastat is a Honeywell L4006A. Only see a high limit setting with a differential.

JohnNY

That is an inefficient setup and an old way of doing things. You should figure out how to get rid of the low limit and let the boiler go idle in the absence of a call for heat.

BillyNYC

would a combination aquastat with a low limit and high limit at least help the situation?

BillyNYC

or any other ideas? im pretty good. at installing and troubleshooting things as I own other properties and have similar setups without this issue that's why this is puzzling me

Seabee5701

Hi. Outdoor reset control. Uses outdoor temp sensor and indoor boiler water temperature and allows temp to adjust/reset by outoor temperature.

Seabee5701

Take a look at tekmar 256 control.....there are quite a few......

Seabee5701

Different manufacturers..

BillyNYC

does this replace the current Honeywell Aquastat?

Seabee5701

Yes

BillyNYC

what about the summer or warmer months? I would have to turn the boiler into pilot only to prevent it from heating the water. Would I still have to do the same?

Seabee5701

Depends. You have to read install. Existing aquastat could possibly remain, it could tie into 24volt control circuit for thermostat.

BillyNYC

basically this is my only way to make this older boiler more efficient without replacing it

Seabee5701

It should save on your gas bills....yes, only other way to gain more efficiency is a modern replacement boiler.

Seabee5701

Above a certain outside temperature, (normally adjustable), it would not run if outside temp is above 50-60 degrees.

EBEBRATT-Ed

@Billy NYC

Post a picture of the controls. Chances are all you have to do is disconnect the low limit you must keep the high limit

EBEBRATT-Ed

You don't want outdoor reset. You have to keep the flue gas temperature above 250-300 to prevent flue gas condensation which you can't do with that boiler. You have to keep the return water above 130 degrees during sustained operation.

Water below 130 is ok only on start up and for a limited amount of time

motoguy128

EBEBRATT-Ed said:

You don't want outdoor reset. You have to keep the flue gas temperature above 250-300 to prevent flue gas condensation which you can't do with that boiler. You have to keep the return water above 130 degrees during sustained operation.

Water below 130 is ok only on start up and for a limited amount of time

I hear this said a lot but I’d like to see data to back it up. I think these heat exchangers have too high of an approach to condense unless water remains under 100F. If you look at efficiency of these boilers on steam vs hot water and you only have a about a 0.5% change in efficiency. Maybe my boiler is just scaled up a bit and needs the flue passages cleaned but I see 300F before the draft hood and over 200 after (when its already diluted with room air). When steaming its around 350/250. Although when I’ve put a cheap combustion analyzer on it, it has excess air.

I’ve also seen high volume/mass converted gravity systems with 40 yo under fired atmospheric boilers run under 100F for 30 minutes and not a drop of condensation that I could see in the flue and no evidence of corrosion.

SO probably depends a lot on draft and how the boiler is tuned.


All that being said, outdoor reset would significantly reduce standby losses in mild weather. The downside is that with fin tube, it will likely short cycle under 160F as there is little mass.... especially once it warmed up since it’s probably already generously size with pickup losses for 180 or 190F.


Normally at minimum, end switches are used to call the boiler in a setup like this. I personally prefer to always use a zone panel as its easier to troubleshoot and cleans up the wiring, and prefer seperate pumps over zone valves.

Leon82

Wouldn't you just use an aquastat for a cold start boiler application?

JohnNY

All you need is a single-function, breaks-on-temperature-rise aquastat. If you're not piped for primary-scondary piping or are using a condensing boiler (you're not) then Outdoor Reset/Tekmar isn't going to help you.

Seabee5701

Billy nyc wanted something to do what a outdoor reset does.....save money. I agree with motoguy. I have installed 2 dozen of these controls on weil mclains with standing pilots...no problems at all

BillyNYC

Thanks for all the information, let me give you some more information on my setup and lets get an even more concrete answer.... 3 different circumstances pumps (1 to each zone), 3 transformer relay switches with an auto/man switch (currently set to auto. all 3 zone relays get power from source, then connect to tstat for each zone and then straight to back of boiler to a two wire x1/x2 connection. Hope this helps. Maybe wiring is off or zone relays are bad and keeps boiler water hot

BillyNYC

sorry CIRCULATOR not circumstances

BillyNYC

here's a picture of the zone relays and the back of boiler

BillyNYC

Any Ideas?

EdTheHeaterMan

The X1 X2 terminals usually connected to a millivolt gas valve connected thru a limit (like the L4006 mentioned) This is the minimum requirements for a safe boiler operation when the boiler was manufactured

The flame safeguard is the pilot on a Powerpile. No Flame ... No GAS. The gas valve has PP and TH/PP terminals to maintain flame safety. The TH and TH/PP terminals operate the main valve and any break in the circuit like the L4006A or whatever is connected to the X1 X2 on the back of the boiler will cut off the main valve.

Now there are probably X X terminals in the zone relays. They are connected to a set of normally open contacts. All three relays are connected parallel so that any of the calls for heat would operate the burner by way of X1, X2 on the back of the boiler.

You will want to disconnect the X1 X2 wires to see if the burner does not maintain the 190° temperature.

If the boiler temperature drops then your problem is in the zone relay boxes.

One of them is fuzed together or (more likely) one of them is not making contact anymore and a repair tech made a temporary repair by jumping the wires together with a wire nut. The temporary repair became permanent when the decision was made to leave it that way. You may have made the decision not knowing it would cost more to operate the heater. The technician may have made that decision without regard for your higher operating cost. This may have been decided many years ago.

BillyNYC

I appreciate your in depth explanation. So if I disconnect the X1X2 wires in the back of the burner and the temp drops then its the zone relays and Im assuming you would recommend replacing them....
What about if I disconnect the X1X2 wires and it still keeps temp at 190? What do I change or troubleshoot then?

This is so puzzling and frustrating that I truly appreciate your help

Lyle {pheloa} Carter

Many of those old hydrotherm boilers especially the millivolt models, had a manual and automatic switch on the side of the triple aquastat. This would allow the boiler to fire like you are describing when the power is off so you could open the checks and Supply heat to the house by convection. Check and see if there is a small black switch, labeled manual and automatic it should be in the automatic position.

BillyNYC

the manual and automatic switch is found on the actual zone relays .. all 3 are set to auto.. nothing is on the actual aquastat other than the temp dial and the differential

EdTheHeaterMan

@BillyNYC Good question. If you disconnect the wires to X1 X2 on the boiler and the burner still operates the burner to maintain temperature. the wiring inside the boiler metal cover is defective. Some may incorrectly say that the wire is "shorted" but it is actually making contact to complete the circuit to the gal valve. this illustration shows that the circuit is completed at the X
where some insulation may have broken off.

We will cross that bridge once you do the test.

EdTheHeaterMan

You will not need to replace all the zone controls. Only the one that's defective. We can Check that by removing one wire at a time starting with the zone relay all the way to the right in the picture. Remove the wire from X1 on the zone control and see if the boiler temperature goes down. After some time if that does not work then remove the wires connected to X1 from the middle control. If that does not reduce the temperature after some time, then remove the wire from X1 on the left control.

This is a process of elimination until we locate the source of the problem. It may be relay contacts on a control or it may be compromised insulation on a wire.

BillyNYC

thank you all... I will test all 3 zones by process of elimination first, then remove the X1/X2 wires from back of boiler to see what happens too..

will update you when I do this