I'm trying to figure out the CEME pressurestat. I'm not getting a consistent hi / low boiler pressure - so I'm worried it's on its way out. I was getting a range between 1.1 and 1.25, but it recently started going up to 1.5 once in a while. I've been trying to get it reset, but don't quite understand how. I thought that the large center screw sets the low end on signal, and then the other smaller screw sets the deadband (or high end off signal). I set the low end ok, but have trouble getting it to consistently turn off at 1.25 / 1.3. Sometimes it will, and sometimes it heads north of 1.5. Not sure if that's a sign of impending doom, or that I don't have the deadband set correctly. My only reference point is loosening the deadband out and then tightening it up to the 'friction point' (like driving with a clutch). Any suggestions?

Thanks
Geoff

The "sticky pressurestat" question comes up frequently on CG and alt.coffee; the stock answer is yes, that's a sign of a failing diaphragm, although you might be able to revive if you gently work the center pin up and down. "Gently" is the operative word as I've also read reports of the owner stripping the screws by overtightening.

By the way, how old is this pressurestat?

The pressurestat was new as of late June...

By working the center pin - do you mean tightening and loosening the center screw repeatedly?

I was also wondering if anyone knew if the center pin and deadband sets the low and high limit or the middle and 'variation'? I noticed that adjusting the deadband would sometimes change the low point of turning on the boiler without adjusting the center pin.

Thanks
Geoff

After spending 4 years, 24/7 operation, with a Mater pressurestat, I can definitely say the sticky diaphragm is not a sign of a failing stat. Mine got stuck in the first few months after I bought the machine. The spare I bought on the occasion is quietly gathering dust, and a couple of times a year I unstick the original stat.

There's good news and bad news:

The good news is that the diaphragm is made of aluminum and simply does not fail -- these stats wear out when the microswitch fails either because of electrical load in a few years (if it's switching the boiler direct) or mechanical failure after a decade (if it's only switching an SSR).

The bad news is that the diaphragm sticks in the "heat on" position. This happens mostly new out of the box, on start up, or in a few hours after, since the diaphragm has had time to freeze in the "on" position. This happens regardless of the stats age; and we have lots of stories of people ordering new ones after an old one sticks and getting the same thing when they started the machine up. This means your safety valve will occasionally get a work out, and you'll get a heart stress test when the machine starts blowing steam. If your heart can't take the stress, get a Sirai and replace it every few years.

You unstick the diaphragm by removing the adjustment screw and working the pin under it in and out with a needle nose pliers. When you hear the micro-switch click back and forth, it's unstuck.

Jack Denver of alt.coffee, who I respect, says the steam side of the aluminum can get slightly oxidized, so that it helps to dunk the stat in lemon juice once a year or so to polish up the diaphragm. The bellows on mine get flooded when I descale, so I've been doing this a couple of times a year willy-nilly. For me the freeze up happens only a few times a year on average, so I'm not sure how big a difference it makes.

On the Ceme, the adjustment screw threads are extremely fragile, so careful. Many people have given up on the Ceme's deadband adjustment, since it doesn't seem to make much difference. Apparently, the newest Ceme models do not have this, and are set on the tightest band possible (around 0.1 bar). The Maters seem to run at 0.15 to 0.2; the Sirais at 0.3 to 0.4 bar.

In any case, these small pressurestats are better performers when used in conjunction with an interposing relay or SSR, than the Sirais, since they have tighter deadbands and a wider adjustment range. LM uses them on their non-electronic steam boilers; so the hobbyist knock on them is simply garbage.

another_jim wrote:In any case, these small pressurestats are better performers when used in conjunction with an interposing relay or SSR, than the Sirais, since they have tighter deadbands and a wider adjustment range. LM uses them on their non-electronic steam boilers; so the hobbyist knock on them is simply garbage.

but they're frickin' loud.

Well.... the screw does strip easily... really, it does! I luckily had a spare without the deadband, but it looks like the range is larger than 0.2. I also had the chance to clean out the vacuum breaker that had been hissing. Just for future reference, when you say 'work the pin up and down' - is that by taking out the center screw and working that black collar up and down, or just screwing the center screw in and out?

Jim nicely defined "working the pin" in his earlier post...

another_jim wrote:You unstick the diaphragm by removing the adjustment screw and working the pin under it in and out with a needle nose pliers. When you hear the micro-switch click back and forth, it's unstuck.

barry wrote:

another_jim wrote:In any case, these small pressurestats are better performers when used in conjunction with an interposing relay or SSR, than the Sirais, since they have tighter deadbands and a wider adjustment range. LM uses them on their non-electronic steam boilers; so the hobbyist knock on them is simply garbage.

but they're frickin' loud.

Yeah. After my second SSR died a heat death, I went with a Struthers Dunn contactor for the interposing relay. Changed back to an SSR as soon as I figured out the derating charts (40 amp job with a built in heat sink got it to 70C, where it derates to 15 amps).

HB wrote:Jim nicely defined "working the pin" in his earlier post...

another_jim wrote:You unstick the diaphragm by removing the adjustment screw and working the pin under it in and out with a needle nose pliers. When you hear the micro-switch click back and forth, it's unstuck.

Oops -- that's for the Mater.

The Ceme has no pin, and screwing **in** lowers the pressure, rather than raising it. For it, just screw it all the way in until you hear it click. On the mater, you have to pull the pin **out** to turn the diaphagm off, which is why working the screw is no help

BTW, it looks like the screw needs a thin handled jeweler's sized philips head so as not to do a number on it.

Thanks another_jim - I thought you were talking about the mater. No matter (ha) - I stripped the old screw and have a new ceme in there now. There was a great deal of oxidation on the brass under the old stat (green patina) so I wonder if that could have fouled the switch somehow.