Boiler control/Circ. pump

Richard Harris

I write from ignorance so patience please. Son-in-law's father has a oil fired domestic boiler and a Jetstream wood fired boiler with two 300gal storage tanks. They are tied together with a two way switch over valve that allows the heat stored in the tanks to be circulated by the oil fired bioler's circulator pump. The ignitor transformer failed on the oil furnace yesterday and we found out that the main circulator pump for the three zones wouldn't start when the thermostats called for heat. This, even though there was fully heated water available from the storage tanks. Since the oil boiler was cold the boiler control would not let the circ pump start.

The question: What is the problem with the circ pump circulating "cold water" through the raditors?

RPH+

STEVE N

It sounds to me...

It sounds to me like the aquastat on the boiler is a triple acting aquastat. This type of control won't allow the main circ to come on until it reaches its low limit setting... remember it is sensing the water in the boiler. You may be able to turn down the low limit setting to kick the circ on when their is a call for heat. I do not know how he is getting his domestic hot water.. if its via domestic coil.. this will cause other problems, like lack of hot water. If he has a water heater this may work. If he does have a water heater you may just want to consider replacing the aquastat with a cold start type. They kick the circ on immeadiately on a call for heat... regardless of boiler temp.

good luck

Steve

Pinball

Does the oil boiler have a domestic hot water coil?

If it does it is more than likely that the boiler also has a triple aquastat. The triple aquastat, has what is called a "reverse acting" aquastat that is tied to the lo limit setting.That is the temp. that the circ will come on and the temperature that the boiler is trying to maintain. to provide domestic hot water.It prevents the circulator form running, and cooling the boiler below that point. to maintain hot water and to protect the boiler from "thermal shock". If your not useing it for wot water than you can turn down the lo limit as far as it will go, and the circ should start.
Hope this helps
Al

Pinball

I guess I don't type as fast as Steve. he beat me to it!

Al

Richard Harris

more info

There is a DWH coil in the oil fired boiler and a second one in the storage tanks. In the winter the DWH is drawn through the tanks then to the boiler. The control is a Honeywell Type L8124A. But what is the theroy on the no circ when the bioler is below the min. temp? Only cold water shock to the boiler?

Rph=

Pinball

Other than wasting electricity

When a boiler's return water temp is too low, the boiler itself starts condensing.While in a special GAS boiler, this might be advantagious and efficient. In a OIL boiler it's downright dangerous for the boiler. Here's why. the waste products of oil combustion, specifically sulphur dioxide, create a very caustic/acidic substance when mixed with water(condensate)This will then eat and distroy the boiler,smoke pipe, and chimney. Until they can produce a no-sulphur fuel the condensing oil boiler is just a dream!
Also , typicaly circulating cold water is not what you want to do. Cold does'nt heat a house very well
Al

lchmb

dont forget

It also helps on the domestic side so that the person taking a shower get's hot water instead of cold.

Richard Harris

Thanks

Yoyr answer is very much appreciated. Let's call it case closed.

RPH+