Oil burner kicks on for hot water but not heat

Reply

  #1  
Old 01-06-18, 06:41 AM
Member
Thread Starter
Join Date: Jan 2018
Location: United States
Posts: 4
Upvotes: 0
Received 0 Votes on 0 Posts
Oil burner kicks on for hot water but not heat

Hi all,

My oil burner is driving me crazy. Every now and then, the burner will not fire and the circulator will not run even though both zones are calling for heat and the thermometer on the boiler reads 170 degrees. If I turn on the hot water at a faucet, the thermometer on the boiler suddenly drops to 150 degrees, and the burner kicks on and resumes operations normally for both zones after returning to around 180 degrees. (During regular operation, it drops to 150 before it fires again and pauses the circulator until it reaches 180 again.) It happened this morning at 3:45 AM and I waited until 4:15, but nothing was happening.

This is a Beckett Burner, with Honeywell control and Aquastat relay (replaced 2 years ago). The high/low is set to 160/180 with a differential of 20. We recently replaced both the oil pump and motor, and changed the oil filter in June. Both wall thermostats programmable, and one of them has a setting which allows for a 1 degree swing in temperature. I can hear both thermostats click when they call for heat.

Any help or thoughts would be greatly appreciated. I'm wondering if it is a fault in the thermometer that is on the boiler itself?
 
Sponsored Links
  #2  
Old 01-06-18, 07:32 AM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 51,891
Received 256 Votes on 241 Posts
Welcome to the forums.

It's not the burner..... It's not the boiler...... or you wouldn't get DHW.

The aquastat maintains boiler temps for the DHW and raises the water temp based on heating demand. It sounds like it doesn't know there is a call for heat. You have two thermostats and one circulator..... that means there are zone valves. Are they opening ?

Pictures of your set up and controls would be helpful. How-to-insert-pictures
 
  #3  
Old 01-06-18, 08:30 AM
Member
Thread Starter
Join Date: Jan 2018
Location: United States
Posts: 4
Upvotes: 0
Received 0 Votes on 0 Posts
Thanks for replying, Pete. I've attached 3 pictures to show our setup. The circulator pump is on the pipe directly below the Taco valves.

I'm fairly certain the zone valves are opening, because once the burner fires after running the DHW, the heat resumes normally without me touching the zone valves. I didn't check if they were open once it stopped this morning. How can I be certain they are opening, other than feeling the pipes to see if they're cold?

Thank you!
 
Attached Images    
  #4  
Old 01-06-18, 10:49 AM
Member
Join Date: Oct 2013
Location: United States
Posts: 2,698
Upvotes: 0
Received 11 Votes on 11 Posts
You have what is known as a warm start control which allows the boiler to maintain temp. if needed or not because of your tankless coil for domestic hot water.

That control also makes your domestic hot water a priority which means if there is a call for heat and hot water at the same time the hot water takes preference and the circulator stops until there is enough temp in the boiler to run both.

Your settings are 160/180 with a diff of 20. which means your burner will come on at 150 and with your 20 deg diff shut off at 170 for the hot water. The 180 is the high limit in case the stats are calling for heat and are not satisfied right away. The burner will shut off but the pump will continue to run and the burner will come back on at 170 until the stats are satisfied.

If there is a call for heat and hot water your pump should be running from 150 to the high limit until the stats are satisfied.

If the boiler temp drops below 150 the domestic hot water takes preference and shuts the heating pump off until the boiler temp rises again.

To check your zone valves on a call for heat push the lever on the zone valve down all the way. If the ZV is working there will be NO resistance. If the stat is calling and the lever CANNOT be moved without resistance you have a problem.

When you turn the stat up there is a slight delay in opening the ZV's so give them a minute to respond.

Hope this helps a little.
 
  #5  
Old 01-08-18, 09:14 AM
Member
Join Date: Oct 2007
Location: Eastern CT
Posts: 150
Upvotes: 0
Received 0 Votes on 0 Posts
That looks very similar to the Honeywell triple aquastat I have on my boiler (w/ thankless coil). In 17 years, I've had two of them go bad. The last time I was able to find another from a place that sold obsolete/NOS equipment for a good price. I have been told that a more modern control can be adapted to do the same thing as this old one and cost a lot less. I haven't dug into that yet to see.
 
  #6  
Old 01-08-18, 11:21 AM
Member
Join Date: Oct 2013
Location: United States
Posts: 2,698
Upvotes: 0
Received 11 Votes on 11 Posts
M,
This is what you would get, if it helps.

L7224U1002, Honeywell

http://www.supplyhouse.com/

Go to the sight above, then click on heating, then aquastats and along the left side of page check off what you want.

This one is electronic and much cheaper and the replacement for what you have.

Unfortunately, I doubt that's the problem this time since that control is common to the domestic water and the other zone that is working.

Hope this helps a little.
 
  #7  
Old 01-08-18, 02:14 PM
Member
Thread Starter
Join Date: Jan 2018
Location: United States
Posts: 4
Upvotes: 0
Received 0 Votes on 0 Posts
Thank you, spott, for that very thorough response. It makes sense to me about prioritizing DHW. I still don't understand why, in the middle of the night, the burner stops firing and the circulator stops running, even though both stats are calling for heat (and have fallen 2-3 degrees below the set point) and no hot water is being used. Once I run hot water at a sink long enough, the burner seems to catch on that it needs to run, suddenly fires up, and the circulator begins pumping again. It's so strange.

I'll check the zone valves the next time it happens to see if they are open while the stats are calling.

Thanks again for your input.
 
  #8  
Old 01-08-18, 05:02 PM
Member
Join Date: Oct 2013
Location: United States
Posts: 2,698
Upvotes: 0
Received 11 Votes on 11 Posts
If it happens again and you find the ZV's are open but the burner is not on and according to the boiler temp should be, go to the control and with needle nose pliers or something jump the TT terminals in the control.

If the boiler and pump start then you may have a problem in the control.

The domestic water runs off the low limit. The heat runs off of TT terminals so the TT does not come into play for the H.W., just the heat and you may have a problem in the TT circuit at the control, especially if both zones are doing it. That circuit is the common denominator to both zones.

Just a thought.
 
  #9  
Old 01-09-18, 09:16 AM
Member
Join Date: Jan 2008
Location: Southeastern Pennsylvania
Posts: 2,947
Received 0 Votes on 0 Posts
Figure 12 on page 7 of this manual shows how the Aquastat works.

https://customer.honeywell.com/resou...0s/95-6571.pdf

It looks like maybe the Low Limit/Circulator is turning the burner ON properly when the temp falls to 150 and then it properly turns ON the circulator when the temp rises to 170 (diff set at 20).

But before that - even though there is a call for heat via T-T - the relays for the circulator and burner are not being closed by the Aquastat. Itís as if the dropping through the low limit and rising again gets you out of the problem. (fig 7 on page 5 shows the Low Limit/Circulator).

So in other word, the Aquastat is bad. I had that Aquastat and now have the L7224U. Whatís nice about the L7224 is you can read out on the display when the circulator and burner are being turned on, etc.

Name:  AstatOp1.jpg
Views: 891
Size:  79.0 KB
 
  #10  
Old 01-14-18, 05:01 PM
Member
Thread Starter
Join Date: Jan 2018
Location: United States
Posts: 4
Upvotes: 0
Received 0 Votes on 0 Posts
Thank you for the reply! If it happens again I'll go with the new Aquastat. Hard to believe that these things could fail at the one thing they're supposed to do.
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes
 
Ask a Question
Question Title:
Description:
Your question will be posted in: