Does anyone have a portafilter fitted with a pressure guage lying about that I could borrow to test the OPV pressure of my Gaggia Classic? I’ll pay postage both ways. Thanks in advance.

Think I’ve got one in the garage somewhere. It’s not the whole portafilter though, it’s just a pressure gauge. You have to unscrew the spout on the bottom of your portafilter and replace it with the gauge. Might need a bit of PTFE tape. Bit of a bodge, but it works. If you don’t get any better offers, let me know if you’re interested.

By the time you’ve paid postage both ways you might as well get one from eBay:

https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F161207194396

Handy to have lurking as a periodic check (annual service and boiler strip) is handy to know everything is still good.

You’ll need to take off the double spout from the Portafilter and use a load of ptfe tape but it works well.

Small tip: it’s not an oil dampened gauge. On each test, take off the Portafilter, empty out the water and put it back on. The extra air volume dampens the pump pulsing and keeps the gauge needle steady. When you hit the button to stop the pump, the air blows out through the 3 way solenoid and the Portafilter fills with water, then when you hit the brew button again the needle bounces all over if you didn’t take the Portafilter off.

Ah cool. I could do with one of those. My Classic is just not right at the moment. Just gushing out no matter how hard the tamp and fine the grind. Not sure what but probably needs proper service, but wondering if the pressure is too high maybe.

Question though is, what is the right pressure (or how would I work that out)?

Strip everything and check the opv valve is actually working. It may be full of scale and not opening. This could cause all the pump pressure (approx 15 bar) to go into the Portafilter and consequently your issue of not being able to control the output through grind or tamp.

Order a seal kit from eBay for about £8.50 and take the whole thing apart (lots of good YouTube and coffee forum guides around to help). Don’t forget a load of descaler too, or citric acid as it’s cheaper and is essentially descaler.

(I’m assuming everyone is using a pre 2015 Gaggia Classic)

Right pressure is 9 bar in the Portafilter when it’s brewing. You can’t measure that, but if you set it to 10 bar static (I.e. with the gauge blanking the Portafilter) then you will get 9 bar dynamic in brewing.

So basically set the OPV to 10 bar with the gauge on the Portafilter.

Where abouts are you aazlad? I’ve got a portafilter one available.
Getting that gauge is a good idea though. You can then backflush against it. It won’t fix your current issue but it’s good practice.
Yes, I’d get some citric acid from Wilko and load up the reservoir with some and run it through. Let it sit for 20mins with the boiler off. Then flush flush flush!
If that doesn’t work, dismantle the OVP as suggested.

Thanks guys. My current portafilter is an old gaggia one which doesn’t have a threaded bottom – just two small unthreaded holes. I think I’ll treat myself to a new portafilter with a threaded base and get the gauge off eBay.

Incidentally, I serviced the machine last week using this kit. Made a huge difference.

Always good to have a pressure gauge. Have you tried to adjust your OPV in and out. Hopefully loosen some gunk if there’s anything on there. Definitely give it a good descale if you haven’t done so already.
Saying that, the OPV is on the cold side…
You didn’t kink any of the return pipes when you did the service? If you did, you’re effectively sending all the pressure to the grouphead

Wowsers. I thought my Gaggia was producing pretty good shots, until now. I just did the OPV mod and the difference is immense. Lovely smooth tasting espresso.

Amazing isn’t it!
Have you got a PID temp controller on it? That is a fairly cheap and easy mod and will also vastly improve taste.