Aquastat failure? circulating pump question

[mjz2]

I have a bell & gossett 1/2 hp hot water circulating pump controlled both by a timer and an aquastat.

I noticed recently the pump is cycling on and off very quickly once it reaches temperature (120 degrees). Is it reasonable that the aquastat is going bad?
It's a Taco 3/4 inch connected directly to the copper hot water pipe.

When the pump first comes on in the morning and circulates water, the pipe will heat up after a few minutes rising to just above 120 degrees. The aquastat will turn off the pump, but after about 10 seconds, starts up again. Then after a few minutes run time, it will shut off, but then start up again after 10 seconds. It will keep doing this for hours until the pump is shutdown by the timer for the night.

The pipe certainly has not cooled off at all during when the timer is on and certainly does not cool off to 95 degrees which would normally trigger a pump start.

Any suggestions on debugging this?

[icy78]

A multimeter and a good way of measuring pipe temperature.

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