Sleep Number beds, QA techniques, and (not) saving $300

We’ve owned a Sleep Number bed since the mid-1990’s – an original two-cell queen, with the original old model wired-remote, loud-as-hell pump. It’s served us well and is still functioning fine after many years of service. When Shymala moved to Connecticut in 2010, she bought a new single-cell full-sized mattress, and took it with her when she moved to Brooklyn in 2012.

This last winter, we moved her Sleep Number bed from Brooklyn to San Jose. In Brooklyn, it had worked fine: it stayed inflated well and was solid and comfortable. We carefully did our research about moving inflatable beds and noted that the consensus was that the bed should be deflated to about 30 (out of 100) while going over the Rockies; the change in altitude would cause the air inside at sea-level pressures to expand significantly, and since the bed was quite new, we wanted to make sure it was going to survive the trip.

We followed the suggested procedure: deflated the bed, check; removed the hose, check; capped it off with the supplied plastic cap, check. Very much like the previous move of this same bed from Connecticut to Brooklyn, which worked just fine. We bagged it up and the movers put it in a box, and off it went to California.

We set it up on the bed frame in the same way it had been used in Brooklyn, reconnected the pump, and inflated it. Halfway through the first night, Shymala found herself all the way down on the slats of the bed frame. The cell had almost completely deflated. We tried it again, and it didn’t deflate as badly, but still too much to be comfortable. We experimented with how much it was inflated, whether rolling around on the bed made it deflate, but couldn’t get any kind of consistent result.

We finally hit on a temporary solution of inflating it to somewhat above the desired firmness, then popping the hose off and installing the cap. This kept the cell reasonably well inflated, but it still deflated slowly over the course of a couple days.

At this point we suspected that there had to be a slow leak in the cell but we couldn’t figure out why. We called Select Comfort, and they were as mystified as we were, which wasn’t encouraging. Their suggestion was that we needed a new cell, so we ordered one. After getting off the phone, we started thinking that since the cell was holding pressure better with the cap on than with the pump, maybe it was the pump instead. So we called back and ordered a pump.

The pump came, and we tested it with the pump. Same result: inflating it to full then waiting resulted in the cell slowly deflating over an hour or so to a setting of 5 on the remote. This meant the pump was not the problem.

The pump’s been used for about an hour, so we thought, “great, we can return the pump since it’s not the problem.” We called Select Comfort to arrange a return. Unfortunately, the customer service reps did not mention when we purchased the pump and cell that any parts you buy are non-returnable.

Let me emphasize that, for anyone else trying to debug a Select Comfort problem: items are 100% non-returnable. Do not expect to be able to swap parts to diagnose a problem.

So there’s $118 gone west, and the bed is still screwed up. They did offer to let us return the cell since the reps hadn’t told us that about the “you bought it, you’re stuck with it” policy. We hung up, and then started trying to figure out how to debug the problem without blowing any more money.

At this point, we could not be sure where the problem lay for certain. Was it that the pumps both had a similar issue that our configuration was exposing, or was the cell really messed up somehow in a non-obvious way? This resembles the case of a client-server problem in software: the two aren’t communicating, and you don’t have a way to unit test the client and server.

We had unit-tested the cell as best we could: we inflated it, and used the cap to simulate the pump sitting there not running. The slow deflation didn’t tell us anything because we weren’t sure that the two situations were exactly equivalent. We didn’t have a way to unit-test the pump (such as a manometer to verify that the check valve in the pump wasn’t leaking). This meant we had to come up with a way to do a better integration test.

After some thinking, we came up with the idea that there was a second Sleep Number bed available with a different model of pump altogether. If we swapped the pumps, we’d know whether the pump had an issue or if the cell did. (If the new pump held pressure on the old bed, the pump was OK; if the old pump failed to hold pressure on the new cell, the cell was bad.)

The test showed that the cell was bad: the new pump held pressure on the old bed just fine, and the old pump slowly lost pressure on the new bed.

Okay, so that meant that if we had opened the cell first, we would have not needed to open the pump at all. Bad guess on our part! We opened the new cell and installed it on the bed. The hose was considerably more difficult to get on the new cell, and observation showed that there were two O-rings that…aw, crap. I finished installing the hose, pumped up the bed, and as expected, it held pressure just fine with the original pump that we’d brought from Brooklyn.

I then went out and looked at the old cell. The attachment had a small groove in it which contained…no O-ring. Apparently when we disassembled the bed in Brooklyn, the O-ring failed or was pulled off. The connection in California had a good-enough seal to inflate the bed and keep it inflated for a while, but not a good enough one to sleep on. We essentially ended up spending $200 to replace a 25-cent O-ring.

Conclusions:

  • Make sure you know baseline conditions before you start testing – the classic “known-good state”. If we’d had a baseline state that included a check for the O-ring, we would have solved this by a short trip to the hardware store.
  • Make sure that your oracle, if you have one, is sufficient. Select Comfort’s customer service does not have a good diagnostic tree available to help them spot this problem, and therefore couldn’t tell us to check for this particular issue.
  • Make sure you know the costs for testing. In this case,  swapping parts to fix a Select Comfort bed is a problem, as everything is non-returnable.
  • Know your problem space. When looking at a pneumatic connection, check to see if there are supposed to be O-rings there and verify that they’re still there.
  • Search for the problem; if you have to solve it yourself, document it. No search turned up “look for the O-ring”, so here’s a tip: if you have an intermittent deflation problem with a Select Comfort bed after a move, look for the missing O-ring first.
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