Roof valley repair -- open or closed?

I'm having roof valley problems with a 15 year old house that I bought last summer. There was little rain in Western Colorado since I bought the house, but this winter leaks showed up in about half of the nine roof valleys from melting snow. The current valleys have metal "W" flashing of the open valley type construction, except that the shingles are butted right up against the center ridge leaving no open channel. Most of the roof is fairly high pitch. I am told that I don't need a new roof, but in the one repair job I had to have done this winter on a low-pitched add-on, there were quite a few torn shingles along the boundary where the old shingles were lifted to slip the new ones under. I'm not sure if this was due to carelessness or the cold weather, or this is just standard for a repair job. I am now trying to decide if should tear out and repair the remaining valleys only or have the entire roof replaced.
I have received conflicting advice about whether open or closed valleys are better. I am somewhat reluctant to put back the same type of valley that is currently leaking in so many places unless there is clear evidence that open valleys are better. Generally the rest of the house has high-quality materials and construction, so I would have thought that the roofing job would have been the same -- but perhaps not.
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Richard wrote:

...
I like closed valleys. I like the looks better. Either can be long lasting under the right conditions. I do suggest a water shield under a closed valley. Not a bad idea for an open valley.
--
Joseph E. Meehan

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You might check to see if the "ears" were cut off of the valley shingles at installation. Meaning the top of the shingle, it's where the shingle would be "pointed" if the valley cuts were not properly made, allowing water to be conducted sideways, literally. Carefully lift a shingle in the valley, and if the underlying shingle comes to a point in the valley, cut off the point using a hook knife, being careful not to damage the metal. I prefer a "one-cut" valley, where the face that recieves the least water (or is of lower pitch), is wrapped up under the opposing face, and the opposing face recieves the valley cuts. Tom > Richard wrote: snipped-for-privacy@mailandnews.com

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