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Oil Boiler build up… Cold start (and run?) problem

gtgoat Member Posts: 2
My house (2200 sq ft) was built in 1925 and I bought it a

few years ago. It looks like the original heating system was a gravity fed coal

fired system. A new Burnham V8 oil boiler was installed in 2000. The large cast

iron radiators and 2+ inch pipes are still being used. Domestic hot water is

supplied by an electric hot water heater. When I open my boiler up for cleaning

once a year it is always filled with red, green, and yellow gooey material that

is difficult to remove. The passages in the boiler are nearly blocked with this


I think the problem is caused by low exhaust (flue?)

temperatures. The system has one zone. When the thermostat calls for heat the

circulator and boiler turn on. The boiler only shuts off when the thermostat is

done calling for heat. The aquastat is a Honeywell L8148A1017 and only has a

high limit control. The high limit is never reached.

I’m guessing that since the house has 14 radiators and the

big steel pipe, the 100+ gallons of water never gets hot enough to reach the

high limit. If that is the case, the flue temperatures never get hot enough and

that is why I’m experiencing the build up in the boiler.

The oil servicing company isn’t much help. He just says to

make sure it gets cleaned every year.

A few questions for the experts:

1. Am I correct about the build up in the boiler?

2. If I don’t do something about this am I shortening the

life of the boiler?

3. If this is a problem I’m thinking that some kind of

mixing valve would work to constantly circulate hot water through the boiler

and “leak” hot water to the rest of the system. Do they make a valve that does




  • Alan R. Mercurio_3
    Alan R. Mercurio_3 Member Posts: 1,620
    Re: Burnham V8

    I don’t think that boiler is supposed to be used as a cold start? I could be wrong? I’m thinking it should have an aquastat that has a high and low limit. Also it sounds like it might need to be piped with a boiler bypass. I’m betting you’re condensing.

    Check out the pages from 26 to 28 of the attached manual and see which applies best to your application.
    Your friend in the industry,

    Alan R. Mercurio

  • meplumber
    meplumber Member Posts: 678
    Flue gas condensation

    Alan is exactly right.

    These boilers do not run well as a cold start.  You also need the boiler bypass to temper the return water above 140 deg F.  I have seen these boilers run as a cold start on small baseboard systems.  However, your system, with its large cast iron radiators and large piping contains a lot of water.  When the circs kick on, the cold water starts to move thru the boiler.  In a system with this much water, it could take quite a while for the boiler to heat all the water in the system above 140 deg F.

    The condensing point of #2 fuel oil on the return water side is 133 deg F. 

    Sorry to say but you are going to have to take it off cold start and pipe in the bypass or you will experience a premature boiler failure.

    Good Luck
  • billtwocase
    billtwocase Member Posts: 2,385
    I'll echo that

    Change the aquastat, make it a warm start, by-pass would help, clean it in the spring after long winter use, and come fall, it won't look like that. The low limit set at 120 will not allow the circ to be pumping ice cubes thru the boiler 
  • gtgoat
    gtgoat Member Posts: 2
    How to do it

    Thanks for the advice. Based on your help I found the Danfoos TV valve and a useful installation document. It references its use on large hot water systems.  http://na.heating.danfoss.com/PCMPDF/ESBE%20TV.pdf

    It doesn't seem like it will be too hard to run a pipe between the outlet and return.

    Is the Danfoos thermic valve the only option that I have? Are there other companies out there with similar products?
  • Steamhead
    Steamhead Member Posts: 16,455
    You might also consider

    an injection-loop setup.

    In this system, the boiler has its own loop from the supply to the return, and its own circulator.

    Likewise, the system loops from return to supply with its own circ.

    Joining the two is a small pair of pipes and a small circ whose speed varies, to inject just the right amount of hotter water from the boiler loop into the cooler water in the system loop.

    The injection circ is controlled from a Tekmar or similar unit that measures the outdoor temp and the water temp in the system loop, and varies the circ speed as needed to inject just the right amount of heat into the system.

    So the boiler will stay warmer without overheating the house.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
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