Hot water/steam is being pushed back into the tank via the return line

[Flo Kraus]

Hello everyone,

After an intense troubleshooting session with my Brewtus (dual boiler), I’ve reached the end of my knowledge — and I especially can’t explain the behavior from a physics standpoint. So I’m relying on your help. Maybe someone has an idea or can explain something to me.

to put it briefly, the questions in general:
- Shouldn't the brew and steam boilers be separated in terms of pressure? Or are they actually "connected" somewhere?
- Could someone check for me if the preassure of the brew boiler is at about the same as the steam boiler (1bar).
-  Should the expansion valve and the air relief valve remain sealed when there is a pressure of 1 bar in the return line?

Problem:

• Hot water/steam flows back into the tank via the return line

• After a few hours, the brew boiler gradually empties — water gets refilled during extraction and it takes some time untill water reaches the group head 

This issue has been ongoing for about a year. I initially suspected a leaky valve due to scale build-up. So I descaled and also disassembled and cleaned the solenoid valve, expansion valve, and air relief valve.
Today I replaced the parker solenoid valve but this doesn't stop the backflow.

Observations:

1. The issue only occurs when the steam boiler is turned on → Only brew boiler heated: no backflow

2. Pressure from the steam boiler transfers to the brew boiler → Steam boiler heats to 1 bar, shortly after the brew boiler also shows 1 bar

   • Note: the brew boiler is filled via a pipe that passes through the steam boiler

   • Question: Shouldn't the brew and steam boilers be separated in terms of pressure? Or are they actually "connected" via that line?

3. Steam seems to push back from the brew boiler (filled from above) → The steam boiler (filled from below) doesn’t empty

4. Steam escapes via the expansion valve → OPV is set to 10 bar, at just 1 bar pressure it should normally remain closed

   • Question: Or is that only true for water pressure and not for steam pressure?

5. Steam also escapes through the air relief valve toward the tank → Return line to the tank gets hot, condensation drips through the vacuum hose

Possible causes (only if the valves should be closed at 1 bar):

1. Expansion valve (Expobar 30400055) leaking or seal surface damaged

   • The OPV is only supposed to open above 9 bar during extraction — which it does

   • If it’s venting already at 1 bar steam, then it’s leaking (backflow possible via steam pressure)

2. Vacuum valve leaking

   • The vacuum valve (Expobar 65000215) is supposed to open during heating, then close?!

   • If it doesn’t close, steam/water escapes continuously → backflow into tank
     

Thanks in advance for all your answers! 😊

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[Ben McCafferty]

Hi Flo—(and deleting the DMT hacked email):

A couple of questions. You stated:

• Hot water/steam flows back into the tank via the return line

Flows back into *which* tank?

By “return line”, what do you mean?

What model of Brewtus do you have, and is it a machine with a vibe pump or a rotary pump?

As to resting pressure of the brew boiler, I don’t know. Mine (Brewtus 2, vibe, modified to rotary/PID) always showed a resting pressure of maybe 3-4 bar, and then I set to 9 bar for extraction.

Steam pressure can be adjusted also, and I usually run about 1.45 bar. Factory setting is closer to 1 bar.

On the steam boiler, the vacuum breaker opens when the boiler cools. It closes when the boiler heats. (Aside—all that fails in this part is the o-ring—I have 100 of them if you’d ever like a replacement—had to order 100 minimum). The pressure relief valve opens at significantly above 9 bar, and is usually factory preset (though I have opened these and adjusted them). Only once ever have I had that one open due to overheating, it should not open normally.

The OPV, as you’ve said, can be adjusted for extraction pressure level, usually around 9 bar.

The only place I can think of where the two boilers are connected is the fill piping (i.e. where they get fresh water from the pump). That solenoid opens/closes as needed to bypass water to one or the other, so that’s one source of leak perhaps? If the water in the brew boiler is at higher pressure (which I believe it is, at both rest and extraction), then I could see the brew boiler’s water perhaps expanding and pushing backwards through the fill solenoid to the steam boiler?

The only other place I can think of there being an interface is the brew boiler line through the steam boiler for preheat, as you’ve mentioned. Could that line have a pinhole leak, allowing water to slowly bleed into the steam boiler?

Your symptom of “takes a long time for water to reach the group head” makes sense—if water is bleeding off the brew boiler (emptying it), when you pull the lever, the boiler fills before pushing through the group.

Hmmm…not sure I helped any, but perhaps some new ideas to consider. Curious to know what you eventually find!

b

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[Eric Christoffersen]

to put it briefly, the questions in general:
- Shouldn't the brew and steam boilers be separated in terms of pressure? Or are they actually "connected" somewhere?

Yes, separate. No they are not connected! Brew boiler never boils, it just feeds brew temp water to the group head. The brew boiler output goes in a tube through the steam boiler, but they are sealed from each other.

- Could someone check for me if the preassure of the brew boiler is at about the same as the steam boiler (1bar).

No, not the same as steam boiler. Steam boiler is at pressure (1-1.4bar depending on your pstat), brew boiler is not boiling, it is pretty much at room pressure. 

-  Should the expansion valve and the air relief valve remain sealed when there is a pressure of 1 bar in the return line?

Return line... there is an OPV before brew head. When brew pressure is too high the OPV opens a bit and bypasses brew pressure (water) back to the cold water reservoir (assuming this is a unit with a reservoir and not plumbed.) The return line itself between OPV and tank cannot be at 1 bar because the return line is open to the water reservoir.

Expansion valve? There is an emergency over pressure valve on top of the steam boiler. That should never be open unless youve got a serious problem like if the pstat is stuck open. It will whistle like a steam engine and gorge steam. The reverse pressure relief valve on the steam boiler should also not be leaking, like... ever. It sets and seals itself every time the steam boiler comes up to pressure.

Problem:

• Hot water/steam flows back into the tank via the return line

If you mean that the return line to the cold water reservoir is bubbling with steam then yeah thats not good at all. Having brew boiler at steam pressure is bad.

• After a few hours, the brew boiler gradually empties — water gets refilled during extraction and it takes some time untill water reaches the group head 

There is a switch to cause brew boiler fill. When brew boiler gets low the pump will activate to fill it. How low is the brew boiler getting? Not good if brew boiler is actually emptying. Or do you mean it takes a while for brew water to reach group head?

This issue has been ongoing for about a year. I initially suspected a leaky valve due to scale build-up. So I descaled and also disassembled and cleaned the solenoid valve, expansion valve, and air relief valve.
Today I replaced the parker solenoid valve but this doesn't stop the backflow.

Observations:

1. The issue only occurs when the steam boiler is turned on → Only brew boiler heated: no backflow

2. Pressure from the steam boiler transfers to the brew boiler → Steam boiler heats to 1 bar, shortly after the brew boiler also shows 1 bar

   • Note: the brew boiler is filled via a pipe that passes through the steam boiler

   • Question: Shouldn't the brew and steam boilers be separated in terms of pressure? Or are they actually "connected" via that line?

Yes separate. Never the two shall meet. 

1. Steam seems to push back from the brew boiler (filled from above) → The steam boiler (filled from below) doesn’t empty

2. Steam escapes via the expansion valve → OPV is set to 10 bar, at just 1 bar pressure it should normally remain closed

   • Question: Or is that only true for water pressure and not for steam pressure?

Do you mean the think on top of the steam boiler? Or the adjustable thing between the pump and brew head? I've no idea how it handles steam. If its able to hold 7 bar brew pressure then I would expect it would be tight against steam. 

1. Steam also escapes through the air relief valve toward the tank → Return line to the tank gets hot, condensation drips through the vacuum hose

 I am not sure what you mean by air relief valve. The reverse pressure relief valve? That is sealed when steam boiler is at pressure. If it leaks it leaks steam into the enclosure, no tube to collect its output.

Possible causes (only if the valves should be closed at 1 bar):

1. Expansion valve (Expobar 30400055) leaking or seal surface damaged

   • The OPV is only supposed to open above 9 bar during extraction — which it does

   • If it’s venting already at 1 bar steam, then it’s leaking (backflow possible via steam pressure)

2. Vacuum valve leaking

   • The vacuum valve (Expobar 65000215) is supposed to open during heating, then close?!

   • If it doesn’t close, steam/water escapes continuously → backflow into tank
     

Thanks in advance for all your answers! 😊

I'm sorry I can't be more help. It sounds like you might have a leak in the brew pipe that passes through the steam boiler. Either that or some of your tubing is routed incorrectly. Is this new behavior? Did you ever see this machine work correctly?

I would try and debug how the pressure is getting from steam boiler to brew circuit because it really shouldn't. You could maybe rig up a fitting with a bike pump to pressurize the steam boiler, then undo stuff and see where the pressure is going?

 

[Flo Kraus]

Hi and thanks a lot for your responses, both Eric and Ben. They really helped me narrow down the problem further and to find a solution (partially).

To keep it short: The issue was a small leak in the riser pipe through the steam boiler, which caused pressure to transfer to the brew boiler.  Since there’s no additional valve between the pump and the brew boiler, the pressure was able to push the water back. I bypassed the riser pipe through the steam boiler, and now the brew boiler isn't emptying anymore — so that's progress!

However, the steam boiler is now losing water. I still got a flowback and every 3-5 minutes the pump turns on and fills the steam boiler.

Looks like I’ll need to open up the machine again in the next few days and investigate further. Stay tuned.

And now. let's answer some of your questions:

Flows back into *which* tank?

By “return line”, what do you mean?

What model of Brewtus do you have, and is it a machine with a vibe pump or a rotary pump? 

It's a Brewtus IV - standard Ulka pump.

 

The only place I can think of where the two boilers are connected is the fill piping (i.e. where they get fresh water from the pump). That solenoid opens/closes as needed to bypass water to one or the other, so that’s one source of leak perhaps? If the water in the brew boiler is at higher pressure (which I believe it is, at both rest and extraction), then I could see the brew boiler’s water perhaps expanding and pushing backwards through the fill solenoid to the steam boiler?

No, it's the other way round -  Steam pressure is set to 1bar and resting pressure of brew boiler should be room pressure - when extracting it's 9bar. So pressure was 

 

Expansion valve? There is an emergency over pressure valve on top of the steam boiler. That should never be open unless youve got a serious problem like if the pstat is stuck open. It will whistle like a steam engine and gorge steam. The reverse pressure relief valve on the steam boiler should also not be leaking, like... ever. It sets and seals itself every time the steam boiler comes up to pressure.

No, I meant the OPV. emergency over pressure valve on top of the steam boiler is fine.

There is a switch to cause brew boiler fill. When brew boiler gets low the pump will activate to fill it. How low is the brew boiler getting? Not good if brew boiler is actually emptying. Or do you mean it takes a while for brew water to reach group head?

It's the other way round -  there isn’t a switch for filling the brew boiler. The solenoid valve is responsible for filling the steam boiler. Filling the brew boiler happens solely by starting a extraction.

 I am not sure what you mean by air relief valve. The reverse pressure relief valve? That is sealed when steam boiler is at pressure. If it leaks it leaks steam into the enclosure, no tube to collect its output.

Number 3 in the explode view. but I don't know the function of that valve. The reverse pressure relief valve works just fine.

 

[Eric Christoffersen]

Well I guess the good news is you know the cause. The bad news is that you have a leak in your steam boiler.

I have a brewtus that has a second switch to turn off the steam boiler. I guess its good because I never froth milk, but in practice I leave the steam boiler on because that line through the steam boiler helps the machine have correct brew pressure and make better shots.

I fear your correct approach is going to be to take out the steam boiler and see about getting that leak fixed. In short term, you've bypassed the steam boiler on the brew path, I guess you could cap off the in/out to the brew line through the steam boiler, then at least the steam boiler couldn't leak out.

I'd love to see photos of the place with the leak. I think the boilers are brass so shouldn't corrode, and mine look well constructed - not sure why there's a leak.

Good luck to you!

[Flo Kraus]

I probably won’t be able to fix the leak in the brew boiler without cutting it open or at least desoldering the riser pipe. So it’ll likely stay bypassed.

Yes, I had to seal off the riser pipe with suitable fittings, as steam from the brew boiler was escaping there.

And I’ve finally managed to stop the backflow into the tank. In addition to the leak in the brew boiler, the air relief valve located directly behind the pump wasn’t sealing properly. I’ve replaced it, and now the machine is running like it did on day one.

As requested, attached are some pictures of the boiler.

And once again, many thanks for the exchange that helped me solve this problem.


Left: capped top side 
Right: disassembled, the bottom side

[Eric Christoffersen]

Awesome. Can you tell me more about the air relief valve? I’ve never heard of that, where is it, what can it do?

Any chance you could repair the route through the steam boiler? Is the leak in the middle? Or along the seams where it enters the boiler?

[Flo Kraus]

I didn’t quite understand it either. Here’s the info from Crem customer service — I had asked them about the function of the valve to understand better whats going on inside my machine:  

The air relief valve is small but very useful. It helps remove air.
Sometimes air gets inside the tubes (for example, after cleaning or if the machine runs without water),this valve lets the air go out, so the pump doesn’t push air but real water.
Definitely, makes the pump start easily.
Keeps the machine safe, if the pump works with air instead of water, it can get damaged, this valve avoids that problem and helps the pump live longer.
If this part fails, you might hear strange noises, get no water, or have low pressure.

Number 3:
 

Unfortunatelly the leak is somewhere inside the boiler, so there’s no chance I can repair it myself.  

[Eric Christoffersen]

Neat I don't recognize that air relief valve. I'll look for it next time I'm in there. I've sometimes had problems with air and if its present my air relief valve is probably due to be renewed. Thank you for the response.

Idea: i wonder if there a fitting that would let you cap each end of the tube that goes through the steam boiler, while also running a line through? Like a press fit fitting but which allows the tubing to still pass through the steam boiler.