Cleaning the anti-backflow (or non-return) valve (Paul L)
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This article is intended to explain what this important component does, highlight symptoms which might identify that it is failing and guide you through how to remove and clean it
What does the anti-backflow valve do?
It prevents water from flowing back through the brew path and into the tank. This is because the Heat Exchanger is at the same temperature/pressure as the steam boiler, so without this valve would over time empty completely (and stall the thermosyphon). Vibration pump machines already have the valve built into the pump, because of the way they work (rotary pumps have no such valve system). Many people with rotary pumped mains plumbed machines may well have this problem and never realise it…because the positive mains pressure prevents any back flow.
What symptoms suggest you have a failing valve?
There are 4 symptoms which really stand out and suggest you may have this problem:
- Does the water from the group seem not as hot as normal
- does water almost immediately come out of the group? If yes then your HX should be retaining water properly, if there is a delay of a few seconds then the HX is not maintaining the heat in the grouphead as effectively as a water-filled HX and having tot bring it in from the tank
- what sound do you hear? If you hear the usual quiet pump sound then your HX should be picking up the water properly from the tank, if you get a hum then a louder rumbling sound hand in hand with a delay in water coming through then your pump is priming and running dry at this point
- Just a hum, it's probably the pump motor trying to prime the pump which will have run dry….sometimes difficulty can be had when priming the pump on a hot machine.
Over a period of time a dry pump (that then cavitates as it primes each shot) is likely to sustain damage so clearly this is not good for your Alex. Bear in mind also that if your problem is caused by hard-water then you are not necessarily covered by your warranty. It is possible that vendors are being asked to service faulty pumps which they are entitled to charge for and look to you to sort out the source of the problem i.e. the water you feed your machine.
Other symptoms to suggest you have a failing valve?
There are some other indicators you can look for.
The Alex requires a large cooling flush and it rebounds quickly if you delay in pulling the shot. Therefore, if your group appears hot as normal and you have bubbling from the grouphead when performing a cooling flush all may appear well. However, a reduction in heat can creep up on you so to understand if you may have this problem I suggest you check:
- How hot is the E61 group to touch? If it is only too hot to touch then it is not hot enough, you should need to pull your hand away sharply to avoid feeling that you will scold yourself if you leave it there for the briefest of moments
- When you have left your portafilter loosely in the group to keep it warm and then fill the basket and tamp, what happens if your fingers around the edge of the tamper base touch the top of the basket ridge? If you can feel heat but not savagely then it is not hot enough, you should need to pull your fingers away sharply to avoid feeling that you will scold yourself
- When you lift the lever for the cooling flush how much water do you need to draw ? If only 2 or 3 oz then it is not hot enough, you should need to flush for 5 or 6 oz before it has really overcome the bubbling and fizzing
Let me just mention one more symptom which I did not realise until after the problem had been overcome. I really wish I had realised this earlier:
- the water tank at the rear of the Alex is warm in normal use because the inside of a coffee machine is warm even in the coolest areas. How warm is the actual water in the tank though? Whilst the tank should be warm the water inside should remain cool
Lastly, you can carry out a simple test to check if your anti-backflow valve is letting by. Investigate the water return feed pipe.
Water return test
If your return pipe is leaking then in a coffee machine where the pipe is fed to the drip tray you will have:
- the obvious disadvantage of an emptying water tank plus the drip tray filling quicker
- the obvious advantage of the rising level in the drip tray being visible.
In a coffee machine such as the Alex where the return pipe is fed to the water tank you will have:
- the obvious advantage of no emptying water tank
- no idea the pipe is letting by as there is no visual indicator (unless you occasionally get a puddle of water underneath the machine).
Look at the picture above and observe the two pipes removed. Basically you loosen them and place an external water container by the side so that you will not be damaging your pump during the test. Place the pipes in the container and lift the lever to draw water in the usual way. Lower the lever then hold both pipes vertically so that the water should stay in the pipes. Watch what happens.
One of the pipes is the return pipe which feeds any water back to the water tank. You don’t need to identify which is which to start with because either:
- water will not rise up the pipes so it doesn’t matter i.e. no water is trying to return to the tank so you don’t have the problem
- water will rise up one of the pipes so you this is the return pipe and if water is rising then yes you have this problem.
There are 3 consequences of this problem:
- inefficient machine operation as outlined by the symptoms which can occur
- potential damage to the rotary pump
- a leaking anti-backflow valve may also leak water underneath the machine
So the repair, let’s move onto it.
Cleaning the anti-backflow valve
To access it you will need to:
- switch off and unplug your Alex
- remove the outer case
- remove the inner top cover
- remove the water tank
- let your Alex cool so wait a while before continuing
- unscrew the Gicar box but thankfully you don’t have to remove any of the connections
- remove the water plate, this is a bit awkward as the earthing is still connected so I tied mine with string
- disconnect the water tank sensor and remember which way the wires went
- All much easier than it sounds but it is a good idea to photograph everything as you go in case you can’t remember something important
- See photo of the tools I used, I don’t recall the measurements but it’s easy enough to work out as you go
By this point you should have everything out of the way which obstructs you getting to the valve. Now comes the fun:
- First the easy bit, undo the silver braided pipe [Dave - I can’t remember what this is called] from the anti backflow valve
- Using two spanners hold the anti backflow pipe and unscrew it by holding one part still whilst unscrewing the other. This requires a lot of sustained force and you will see that the whole brew boiler wants to flex so care is required. I placed the hammer in the gap to the side between the front case and the boiler for no other reason than to create some resistance and help avoid something unwanted giving way
- The copper nuts unscrew but I made the classic mistake of my hand being above the rear edge of the chassis so as the nut gave way my hand went down with considerable force onto the case. I was fortunate to escape with bruising but I suggest that you do what I did not - place a folded tea towel across the rear case to cushion any such incident and preferably have your hand further forward or further back!
When the nut lets go be careful to take out the valve slowly and without it falling apart. I found that heavy, sticky water came out i.e. residual descaling solution despite my having flushed through plenty of water for a day or so before this repair. It was another reminder of the the slow nature of water related issues. Problems can take weeks or months to reveal themselves and so can cures such as clean water properly flushing through descaler sitting in a place such as the anti-backflow valve underneath the boiler.
What will you will find inside:
- You may see a large limescale build up inside the valve components. You may not and in my case it all looked reasonably clean and easy to miss any problem
- You may see a piece of grit or other obstruction. There may be nothing obvious
- You may see a badly worn washer. //Perhaps a deformed washer in the way a conventional water-tap washer might erode. Again this may be fine as mine was
Another Alex owner reported seeing small grit thought to be of the kind that can be released by jug filters.
- Clean all components thoroughly with descaling solution and then carefully re-assemble. The ‘seal’ was broken when you undid the valve so to obtain a water-tight re-connection you should use something such as PTFE tape
- It is very difficult to get your hands under the machine to neatly wrap PTFE but you will manage okay with care. I was concerned that I had made a lousy preparation for the nut by having too much PTFE or it being badly wrapped but all was fine.
- Carefully screw it all back together using the two cheap adjustable spanners I found it tightened up just fine and very neatly.
I found the repair fairly straightforward to undertake thanks to good advice on the approach to take. As I really had not found anything of note I thought that perhaps the problem would remain. Thankfully, this repair resolved all of the symptoms I mentioned earlier. I ran my Alex with the case off for a day to observe the repair, look for water leakages and check underneath the case looking for tell-tale signs. All was fine.
Postscript - thoughts about water
This problem arose in conjunction with some others which were also hard-water related. As a result, I installed an RO system before undertaking the repair so that when I switched my Alex back on it would not have to use hard water again and no more aggressive descaling for me in future. I really think the effect of water is an important issue and you can read more on it here
In fact, take an other look at a couple of the pictures and you can see water stains due to various causes over time in the first picture. In the second picture you can see some of the cleaning I did using a descale solution by brush and then water spray to rinse it away.