Boiler tempurature drop

I have a new efm 520, and a honeywell L7224 (or something close to those numbers) aquistat. I set the differential on 25 degrees, low temp is set at 160. My pump only runs for about 4 minutes before the boiler tempurature drops to 135 and shuts it off. Then it takes about 8 minutes to recover back up to 160. This doesn't seem very efficient. I feel that the pump should stay on longer to pump water to all the radiators. I had the stoker set at 3 - 3.25, but I just jacked it up to 7-6 because my furnace ran for 5 hours this morning and my house wasn't heating up.
I don't have a large house, it's an old 2 story with about 1600 square feet of living space. I only have 9 radiators. The variable in this whole thing is my plumbing, for some reason there are 2 inch steel pipes in my basement, they are used for the main lines for the hot and return lines. I think they fill up with a lot of water then the pump shuts off and I have a lot of hot water sitting in those big pipes.
Any input would be great. Should I have a bigger pump? A better fire?

Are your pipes insulated? 2" pipe makes for one big unintended radiator. BTDT All that cold water in those pipes is getting dumped in the boiler and cooling it down quick. Wait and see what your feed rate change does.

Does the boiler have a bypass valve? I think the cold load is dumping the boiler temp and causing short cycling. A bypass valve would help keep the boiler temp more constant.

I agree with Freddy. If you have a bypass valve open that up some.

Is this steam heat or hotwater baseboard?

The large pipes are not insulated. I will probably do that before the real cold weather comes.

When my father in-law and I installed the boiler we didn't see the need for a bypass valve...now I know what it would do for me. He didn't have one on his boiler so we wrote it off as something that wasn't necessary. But he has soft coal hand fed boiler. Anyway, I don't have one, I'll consider putting one in next year.

This is a hot water, radiator system.

Thanks for all your replies so far.

What you have is a very poorly done coonversion from steam to hotwater . Those 2" pipes in the basement are pulling all the hotwater out of the boiler and filling it with the cold water of your radiators but since the pump is running such a short amount of time the radiators aren't even seeing the temp of water desired. I think you are going to use double the fuel normally needed to heat a house that size with out the bypass valve and way oversized supply piping.

When he said 2" pipe, it rang a bell. I just installed a AA130 with steam and know all about 2" and 1 1/4" pipes too well. Do they run a 2" circulator pump for that? There has to be a real lot of water in that system.

I doubt it was a steam system unless he changed the radiators. Older hot water systems were gravity circulated and needed the larger pipes. I don't know how much water your boiler holds but those 2" pipes hold alot. Insulating should help some. I'd lower the differential so that your boiler fires earlier also.

Time for a bypass valve.

I have an idea...maybe I should install a bypass valve I will probably need to drain my system though, because I don't have room on the other side of my return shut off. I hope this works...
Thanks for all the advice. I'll probably get to it next Saturday and let you know if it is working better. Thanks again.

Terry If it was an old 2 pipe steam sytem all you would have had to do was remove the steam traps and add a circulator to the boiler's out side, an expansiontank/filltrol and balancing valves to each radiator. The only problem with doing this is the inefficiency factor. 1" copper pipe holds roughly .04 gals per linear foot however 2" copper would hold something like .16 gals per linear foot of pipe if my math is correct .