Boiler cycling on high limit

Roy Tenn

Hi All,

I was working on a boiler today that was cycling on the high limit. I would just like to know if this is normal(I am mostly a forced air guy). This is a Raypak boiler model
255WTB-N, standing pilot and uses a Grundfos (UP 26-46F)pump. The pump run continuous.The tstat is in series with
the high limit which is set at 190*. The pump is ok because I checked it and I can hear the water moving.The customer is complaining the gas bill is too high.Is this cycling normal and what can be done to rectify this problem. Any comments and suggestions would be appreciated. Thanks in advance.

Roy

eleft_4

cycle

The call for heat is on the high limit , 8124 10* differential, 7124 (electronic) 15* differential.

HTH,, al

hydronicsmike

You said you checked the flow, but to me...

...it seems that this is typically caused by flow problems (no flow, circulator could be sitting there stuck and humming)or if the Boiler T-T is always energized and no call for heat exists (BTUhs not being absorbed by the heating system).

If he doesn't have an Outdoor Reset Control, you may be able to upgrade him and help him to fuel savings and increased comfort level and efficiency. Most Reset Controls (I am familiar with) offer an automatic Boiler Differential that changes based on load as well to minimize short cycling.

www.tekmarcontrols.com

Hope this helps.

Mike

lchmb

curious

Is this something that has just started, been an ongoing problem or is this a new install?

EBEBRATT-Ed

Since the raypak is a coil boiler and holds so little water it is more sensative to lack of flow. If the circulator is to small, piping restricted etc it will trip limit repetedly. I would install a primary pump for the boiler to connected to supply and return. Size pump for 10000 btu/gpm net boiler capacity and install two tees in primary loop to circulate through the baseboard with the secondary pump.

Tripping limit will kill the fuel bill

jim lockard

pressure

You say you can hear the water moving? could it be tthat you are hearing air in the system?(gurling) Whats the pressure on the boiler? should be 12 psi or better up to about 23psi is ok for a 2 or 3 story home. Check the highest rad or baseboard and make sure you have water and that they are up to tempture. If no water or not hot then bleed til you get water. Watch your pressure do not let it get to low, make sure your water feed valve is working and not clogged. If you have more then one zone check and bleed each zone. Best Wishes J.Lockard

Roy Tenn

boiler cycling on high limit

The owner bought this property 2 years ago. I dont know the
history, but she did say the pump was replaced 1 year ago.
This is a 3 storey home used as a rental property. The pressure on the boiler is 20 psi and all the rads in the house are hot.

Roy

lchmb

I would

I would start by pulling the circ and checking the impeller. After that I would purge the system completely and then keep a close eye on the circulator and circ control. I have seen system's do what you describe and find the circulator is cycling on and off due to a bad aquastat or zone control. It doesn't alway's show itself when your standing there which is what make's it fun to find..

EBEBRATT-Ed

Could have put the wrong circ in when it was replaced.