Old grav w/pump cycling frequently

Dale

Since you have the pump on continous flow, good idea too, there are only 2 things that make the burner turn on and off, the aquastat and the thermostat. I would find out which one is opening, so I'll guess the thermostat and turn up the anticipator to max amps to reduce the cycle time, and of course where is the stat located, near a rad? If you jumper the stat to see what happens and watch it,how long before the aquastat opens, I think the 150 temp setting is too low, I would try 190 or so with an old gravity conversion, the trick is to figure out which component is causing the short cycle.

Rufus Laggren

We have an old house that had gravity heat installed, probably in the 40's. 3 floors. Late seventies (?) my parents converted to a natural gas pumped system. It's worked more or less for quite a while. However, now we rent it and details got more critical. I have had to do a lot of radiator bleeding have gotten somewhat familiar with the system.

It still more or less works, but I'm wondering at the way it cycles on/off every 5 minutes or so. The boiler is an AOSmith berkay unit (225k btu), BG pump into a 4-way contraption mounted on the boiler. I eventually wired the pump for continuous run to keep the heat up in the radiators, reduce the cycling wear on the pump, and stop the "thump" when the pump cut in and out every 5 minutes (the installation is right beneath the main bedroom...). Water maintains between 140-150F. There's some kind of bypass at the valve (which is mounted on the boiler and incorporates a make-up feed with a tank).

I have 2 thoughts on slowing the cycling:

1) Can I set it up with a 4-way valve that will switch fully (all "up" or all "down") at 2 preset temps? If so, I can pump the delivery system (mains) and only divert through the boiler when the water drops to a set point. After the water comes back up to the cut back point, the 4-way would switch back, the boiler would shut down, and the pump would only be circulating the water in the mains. This needs one pump and a good valve. It assumes that there is enough fluid mass in the existing mains to stay warm for 20 minutes or more (in average conditions).

2: Add a large insulataed storage tank, pump the tank water through the mains, and pump the boiler circuit through the tank occasionally when the tank temp drops too low. Two pumps, no valve, various temp sensors, large tank (but theres lots of space down there. Or add the storage tank to solution 1.

It hasn't been a glorious experience with the local "pros" (Chicago, near north suburbs). They range from the clueless to the guy who wanted to sell us a new commercial gravity system. That whole experience was somewhat disappointing because of the apparent lack of any real straight information. A few years ago we dealt with another firm which tried to replace the control circuits - they ordered the part and when they tried to install it, informed us that, yes, it was the right part, but that no, it didn't fit for some reason and they put the whole thing back together and left. Oh well. They only billed for a nominal service call, so I'm no complaining to much. It'd just be nice to get a full consistent believable assessment. It may be an art, but it's not rocket science. I'm a plumber by trade, and I have some idea what a competent tradesman should be able to offer in the way of information and maintenance options.

Other info. It's an upfeed. The main has tees both off the top and side - I think it's 2 single pipe loops because there isn't a return running near the mains. 2 heated floors, 4500 SF. 6 to 8 radiators per floor, one 'stat on the first floor.

Thoughts and comments appreciated.

Rufus

Rufus Laggren

> Since you have the pump on continous flow, good

> idea too, there are only 2 things that make the

> burner turn on and off, the aquastat and the

> thermostat. I would find out which one is

> opening, so I'll guess the thermostat and turn up

> the anticipator to max amps to reduce the cycle

> time, and of course where is the stat located,

> near a rad? If you jumper the stat to see what

> happens and watch it,how long before the aquastat

> opens, I think the 150 temp setting is too low, I

> would try 190 or so with an old gravity

> conversion, the trick is to figure out which

> component is causing the short cycle.



Dale,

Thanks for that heads up about possible causes. And I _know_ better than to make assumptions! It appears the thermostat is at least part of problem, so clearly I start there.

Happy Holidays. Rufus

Rufus Laggren

Dale,

Thanks for that heads up about possible causes. And I _know_ better than to make assumptions! It appears the thermostat is at least part of problem, so clearly I start there.

Happy Holidays. Rufus