Boiler safety valve triggered

Equipment doesn't work? Troubleshooting? If you're handy, members can help.
Supporter ❤

#1: Post by emradguy »

Hey guys,

I'm looking for some help with my Duetto II. I have noticed steam hiss from the boiler safety valve for the past few weeks, and haven't figured out why yet. At first, I thought it was the fill probe (because I've had that issue before), but when I pulled it for cleaning, it was in good shape. I gave it a good scrub to really brighten it up and reinstalled it...and of course the problem persists. This am, I noticed the boiler temp fluctuating a lot on the PID. It's set at default of 256°F, but now hits 260 (at which point the safety valve opens), and then with a couple of seconds starts dropping. It goes down to about 250, before climbing back up. The steam boiler pressure gauge seems to be responding appropriately to the temp fluctuations. It seems to take about an hour before the machine loses enough steam to trigger an auto fill.

I have a decent multimeter, and some semblance of how to use it, if needed.

Thanks in advance,



#2: Post by JRising »

Is there steam escaping the safety valve even while the steam boiler is well below the 256? If it is a constant leak even well below where it should open, then I strongly suggest replacing it (Not just cleaning it). They're cheap and if it's old enough to have developed a constant leak it's time. They're called "Safety" for the obvious reason, don't simply disable it, or tighten against the spring beyond the point where it leaks.

Secondly, if your temperature fluctuation ( I won't call it deadband if it's not pressostat controlled) is getting wider, let's find out why.
If you set the steam-target on the PID 5 degrees lower, does the amount of fluctuation stay the same, just 5 degrees lower from extreme to extreme? Assuming you haven't changed your PID parameters, this could be caused by calcium build up on the element and thermoSensor, insulating it just enough that it stays on too long heating the calcium which in turn heats the water too long and the sensor too late after the PID signal is off. You could run a mild descale on the steam circuit to see what condition the solution comes out in. The Element in the Duetto is controlled by the PID via a solid state relay. Solid State relays don't get "Sticky" and have an ever widening deadband as they get old, like electromagnetic contact relays, so I don't think the issue is with the relay, nor the PID if you haven't changed the parameters.

Anyway. Replace the safety relief valve if it has a constant leak even below 250 degrees and post again if you want help with the temperature fluctuation issue.

Supporter ❤

#3: Post by emradguy »

Thanks. I've already got a new safety valve on the way. I ordered it yesterday, and it's due to arrive next Monday or Tuesday. Like you said they're cheap, and there to keep the boiler from exploding, so I'd rather replace it than tear it down and clean it...even if that was all it really needed.

I'll play with the temp setting on the PID Friday, as you've suggested and report back. I haven't changed any PID settings in a long time. I would be surprised if there's scale buildup. I've had it plumbed through a Mavea filter for several years now, with good control of the GH, KH and TDS (all within SCA standards). Though, I have been unhappy about the pH, which is too low and corrosive, such that I've also got new filtration on the way (switching to Everpure Softener).

Supporter ❤

#4: Post by emradguy »

So, my new boiler safety valve arrived yesterday. I've not yet installed it.

The hiss and auto fill triggering are still there, as is the temp fluctuation. I lowered the steam boiler temperature setting to 250°F. The temp is fluctuating between 249 and 253, and the pressure gauge is fluctuating accordingly, dropping down below 1.25 and rising a bit over midway between 1.25 and 1.5. So, the temp fluctuation is a smaller band at the lower setting of 250. Not sure what that means? I guess I could replace the safety valve and then see if that changes? However, I'm thinking while I have the machine open for the safety valve replacement, I can pull the temp sensor and inspect that, if you think it would help...or anything else.

User avatar
Randy G.

#5: Post by Randy G. »

I have read a few posts that state the safety valve is hissing, and the descriptions often sound more like it is the anti-vacuum device. Just saying... It would seem like anti-vac valves are cheap and safety valves maybe not so much, but I have not checked prices myself because I have never had that problem.
Espresso! My Espresso! -
LMWDP #644

Supporter ❤

#6: Post by emradguy »

Yeah, I've read those too Randy, but I removed the cover and confirmed it was indeed the safety valve.

Supporter ❤

#7: Post by emradguy »

I replaced the boiler safety valve today, and of course, the hissing has stopped. I was going to leave the steam boiler temp at 250, but accidentally reset it to defaults by not holding the left button down well, and just decided to leave it. So, the steam boiler is now set back to 255°F. The temp is fluctuating between 253 and 258.

I gotta say, I don't why the safety valve popped, and if it was something less important, I probably would accept it as a fluke and move on. However, I do find it a bit concerning.


#8: Post by JRising »

Remember that a boiler Safety Valve should open any time the boiler exceeds its recommended pressure. It doesn't actually mean for sure that the boiler has over-heated. The boiler could have been over pressured by a temporarily leaking boiler-fill solenoid or calcified level probe... Probably a third thing I'm not thinking of.
If it seems fixed, keep an eye on it, but don't worry about it. Enjoy the machine. It either will or won't prove itself to be okay. You get to enjoy good espresso in the mean time.

Supporter ❤

#9: Post by emradguy »

Thanks, man! I've been down both the faulty solenoid and scaled fill probe before. Both of those manifest as water all over the counter and floor. So, I'm happy that hasn't happened in this case. Though, now I have some experience in fixing those things ;-).

Yesterday my Everpure softener cartridge and head arrived, so I'll be swapping those in for the Mavea soon. Fingers crossed I get similar GH, KH & TDS readings with it, but without the added effect of a low pH. I also picked up an LM test kit so I can check chlorides and iron as well.