Boiler Cycles?

TK03

What is the heat anticipator (if adjustable) set at on the thermostat? It needs to match the control it is connected to. Turn it up and see if it gets better. If so turn it up some more. If it's too low the unit short cycles. If too high the home overheats and cools off too much before it comes back on. I would start around .4. If it does not have an anticipator check your cycle rate. Follow the instructions which were supplied by the manufacturer of the thermostat for an oil fired steam boier. The pressuretrol should shut down around 2PSI and fire back on at .5.

helium

Boiler Cycles?

I've got a weil-mccan oil fed steam boiler. I've just replaced the thermostat, and a noticing that the boiler will turn off before it's reached the set point. After a bit it comes back on. If it's going from very cold to hot, it does this a bunch of times until it gets to the temp. I've set it to.
Is this normal?
It's almost as if the boiler is "resting" on the way up to temperature.
The cut-off is set to .5psi, but I've never seen the pressure gauge move. I know it's working, as the boilder was maintained last winter, and it all checked out ok.

superMARKet

That's supposed to happen

The pressuretrol (or vaporstat) is doing its job. Just because pressure isn't registering on the gauge doesn't mean that there's no pressure in the system. Once the system is filled with steam, and the main vents and radiator vents are all shut, you've got the maximum volume of steam you can handle. If you make steam faster than you condense it (which you typically do), there's no place for the steam to go, so you build pressure.

0.5psi is low enough for many gauges to not be able to sense, especially ones with a 15psi range or more. The gauge might also be broken, or its siphon loop might be clogged, or it might not be on a siphon loop at all. (I hope your pressuretrol is!)

Are you sure you've got 0.5psi cut-OUT and not cut-IN? If so, chances are you've got a vaporstat (good for you!) That's a pretty low setting, but if you've got heat everywhere, then it's great. If you're really working with 0.5psi maximum pressure, you might never see the needle on the gauge budge even if everything's working.

helium

re: that's supposed to happen

Thanks, Mark.
It IS a cut-IN, not off or out. It's set to .5psi, as recommended by the oil delivery/boiler maintenance guy. I don't know anything about pressuretrols or that, but I've attached a photo so you can see what it looks like.

-Brian

superMARKet

Yup, that's a pressuretrol

Keep it set to the minimum, 0.5psi cut-in and 1psi differential. No surprise that you don't register pressure on that 30psi gauge.

The thermostat current on that oil primary is 200mA, so if you've got a thermostat with an adjustable anticipator like Jason suggested, and if it's wired directly into the burner (looks like it is), start at 0.2. But don't be afraid of a little bit of cycling on pressure. As long as you're not overshooting the setpoint, I'd rather cycle on pressure than on the thermostat.