Rocket Giotto Losing Pump Pressure

#1: Post by **wlaughto** » October 14th, 2020, 2:32 am

I have a Rocket Giotto (Classic I believe) which is around 14 years old. Has been serviced reasonably reguarly.

Recently, the pressure drops pulling a shot. It works fine for a short time (about 10 seconds) and then is just a trickle. Without portafilla, water streams thru the group head correctly. Also, does not seem to be losing boiler pressure, only pump pressure.

I have changed the pump and still has the same behaviour. Reading other posts of similar nature, points to controller which is an expensive attempted fix if not the issue.

Have read thru this post (Rocket Giotto loses pressure after 30 minutes), and while is similar problem, hopefully not the same.

Any advice welcomed before I start replacing controller!

#2: Post by **nahau** » October 14th, 2020, 6:49 am

Have no idea what a Rocket Giotto "Classic" is and apparently neither does Google. I can find a Cellini Classic. In any case, how's the pressure with a blind portafilter? Are you able to get 10 bar... or whatever your OPV (I'm guessing it has one) is set at? It could be the OPV is leaking pressure sooner than it should... possibly a leaky seal. Also, the thread you linked is talking about "boiler" pressure, and you're apparently talking about "brew" pressure since your talking about pulling a shot. What gauge are you looking at that's dropping? Sorry, I know nothing about Rockets.

#3: Post by **JRising** » October 14th, 2020, 7:56 am

I'm making the assumption that you're not actually measuring pressure anywhere, but just watching the flow coming from the portafilter as evidence that there is pressure at the grouphead. A 14 year old Giotto wouldn't have a brew-pressure gauge, you know this but future readers may not.

When the flow decreases after 10 seconds or so, it it abrupt or does it taper off for a while until it's just a trickle?
Does the pump get progressively quieter as the flow slows down?

With a blind filter in the portafilter, does the pump go silent and stop moving water or does it pump sufficient flow over the expansion valve? (ie. do you get a couple ounces coming out the second reservoir hose in about 30 seconds?)

October 14th, 2020, 7:06 pm

nahau wrote:Have no idea what a Rocket Giotto "Classic" is and apparently neither does Google. I can find a Cellini Classic. In any case, how's the pressure with a blind portafilter? Are you able to get 10 bar... or whatever your OPV (I'm guessing it has one) is set at? It could be the OPV is leaking pressure sooner than it should... possibly a leaky seal. Also, the thread you linked is talking about "boiler" pressure, and you're apparently talking about "brew" pressure since your talking about pulling a shot. What gauge are you looking at that's dropping? Sorry, I know nothing about Rockets.

Pardon my ignorance, but what is an OPV - something Pressure Valve I am guessing?

Only has boiler pressure gauge, which does not change significantly when pulling a shot.

Can only tell that it is losing pressure by the amount of coffee coming thru the the portafilla and a change in the noise of the pump.

Interestingly, I pulled the group head apart and cleaned it a bit and put back together without changing washers/o-rings (or lubricating - no human grade grease atm). I must have not put it back correctly as there is no 'backflush' when turning off the shot, but the pressure coming thru the portafilla is reasonably constant. It does however have a couple of 'pauses' for a miniscule amount of time and takes off again!

October 14th, 2020, 7:12 pm

JRising wrote:I'm making the assumption that you're not actually measuring pressure anywhere, but just watching the flow coming from the portafilter as evidence that there is pressure at the grouphead. A 14 year old Giotto wouldn't have a brew-pressure gauge, you know this but future readers may not.

Correct

JRising wrote:When the flow decreases after 10 seconds or so, it it abrupt or does it taper off for a while until it's just a trickle?

It is abrupt. There is also a couple of miniscule pauses when it starts up and prior to losing pressure.

JRising wrote:Does the pump get progressively quieter as the flow slows down?

Yes slightly. Pump has been replaced.

JRising wrote:With a blind filter in the portafilter, does the pump go silent and stop moving water or does it pump sufficient flow over the expansion valve? (ie. do you get a couple ounces coming out the second reservoir hose in about 30 seconds?)

Not sure about this, will have to check when I reassemble Group head correctly (see above post).

October 14th, 2020, 8:54 pm

JRising wrote:When the flow decreases after 10 seconds or so, it it abrupt or does it taper off for a while until it's just a trickle?
Does the pump get progressively quieter as the flow slows down?

With a blind filter in the portafilter, does the pump go silent and stop moving water or does it pump sufficient flow over the expansion valve? (ie. do you get a couple ounces coming out the second reservoir hose in about 30 seconds?)

Ok, just reassempled the Grouphead (correctly - doh). With blind filter, water pumps ok for a while then, dies off. In fact, there is now a very inconsistent action each time I test, with either a coffee shot or blind filter. Quite a bit of start then stop for several seconds restart the stop again for several seconds, then pump pressure drops. However, nothing is very consistent.

Not sure how to see if if water comes out of second reservoir hose - I assume take machine apart? That is my next step (again).

Does any of the above give you any more clue - controller, pressure stat etc?

#7: Post by **nahau** » October 15th, 2020, 1:02 am

wlaughto wrote:Pardon my ignorance, but what is an OPV - something Pressure Valve I am guessing?

OPV stands for Overpressure valve. You use this valve to adjust the pressure you want to pull shots at... ie, if you want to pull at 10 bar, you adjust the OPV to release at this pressure... if you want to pull lower or higher, you adjust as needed. A blind portafilter is used while making the adjustment. If an OPV is leaking or not sealing correctly, it can release pressure immaturely and give you low brew pressure. John is alluding to the same thing by calling it an "expansion valve"... thus his question about water coming out of the second reservoir hose (the return hose).

There are several things that can cause low brew pressure, or a drop in pressure... OPV, pump, check valve, grouphead. As John is helping you, I will defer further questions to him. I'm sure you guys will get it going! Good luck!

#8: Post by **JRising** » October 15th, 2020, 8:13 am

wlaughto wrote: Not sure how to see if if water comes out of second reservoir hose - I assume take machine apart? That is my next step (again).

Maybe I'm not picturing your Giotto correctly in my head. There are 2 hoses from the machine into the water reservoir, correct?

If so, one goes to the pump and is how the machine takes in water. The second is a return hose from the Over Pressure Valve sending the excess flow (when pressure in the brew circuit exceeds 10.2 Bar or some set pressure) back to the reservoir. With the blind filter in, the water in the brew circuit has nowhere to go except over the OPV, so if the pump is performing properly (Able to pump 65+ ml in 30 seconds against a backpressure higher than 10 Bar) you should be able to see a couple oz of water pouring out of the second hose if you lift it above the waterline in the reservoir.

#9: Post by **JRising** » October 15th, 2020, 8:25 am

Sorry for the multiple-post spam, but another thought just whistled through my head...

It is possible on the old Gicar unit that's in your machine for it to try to fill boiler while you're pulling a shot. That Gicar doesn't monitor the position of the lever... One trick to rule out the possibility of the machine trying to "Boiler Fill" while you're brewing is to slightly overfill the boiler right before pulling a shot. When facing the machine, your right-hand side is the side where the boiler's level probe is. Lift the right side of the machine 3/4 of an inch or more up to an inch and a half and slip a cuttingboard or the handle of a kitchen-knife or something under the rear foot to hold it up like that until the boiler finishes filling to its new "slightly overfilled" depth. Then when you set the machine flat on the counter again, there's no chance of it trying to fill the boiler while you're brewing.
Further explanation. When brewing, the pump is forcing the water into the machine fighting against the backpressure of having to force water through the grounds in the portafilter. It builds 9-10 bar pressure to be able to force the amount of flow through the grounds that you see while brewing. If the Gicar decides to do a boiler fill, it opens a valve to the boiler which is only 1.2 Bar of backpressure to overcome, all of the flow takes that nice easy path, the pump noise changes as it overcomes less backpressure and there's no flow through the portafilter.
Does this maybe describe what you're experiencing?
If after doing the "Overfill before brewing" experiment, the problem goes away for a while, let us know. We'll get into cleaning your boiler fill probe and other suggestions that may limit the occurrence.

October 15th, 2020, 6:38 pm

nahau wrote:OPV stands for Overpressure valve. You use this valve to adjust the pressure you want to pull shots at... ie, if you want to pull at 10 bar, you adjust the OPV to release at this pressure... if you want to pull lower or higher, you adjust as needed. A blind portafilter is used while making the adjustment. If an OPV is leaking or not sealing correctly, it can release pressure immaturely and give you low brew pressure. John is alluding to the same thing by calling it an "expansion valve"... thus his question about water coming out of the second reservoir hose (the return hose).

There are several things that can cause low brew pressure, or a drop in pressure... OPV, pump, check valve, grouphead. As John is helping you, I will defer further questions to him. I'm sure you guys will get it going! Good luck!

Thank you