Unexpectedly cold rooms in zone-valved big house

Howdy, all!
My 83-year old father is worked up (and my mother not worked up but cold) about parts of his almost 100-year old house in a Philadelphia suburb remaining unexpectedly cold.
History: The original system is almost 100 years old, now with a 15-year old large natural gas large furnace. Long ago (>20 years ago) the original circulator motor burned out at an inconvenient time. Told that many systems in older houses could run by convection (or gravity feed?), we tried that for a day and (by jiminy) it worked--the response time for a room to heat was not discernibly different than with a functioning circulator pump. So the system was left that way (with the circulator motor path out of the circulation loop).

We (my brother, my father and I) this summer replaced 13 (!) old burned-out Thrush zone valves on 1 1/4 inch copper pipe (mostly) with new Honeywell 3/4 inch copper valves and fittings.
We painstakingly tested all valves and joints for proper functioning and no leaks. All fine (eventually).

Now parts of the house are unexpectedly cold (it's 15-20 F outside). House: 3 storeys + basement, radiators, very large (4 fireplaces--not used often, with flues currently closed).
My father suspects the added flow impedance due to the reduced-diameter zone valves is causing the problem.
My argument: (i) by definition, there is probably no more than 1 zone valve per zone--they're not in series (I would assume that's the *point* of having zone valves), (ii) why are some parts of the house (presumably under zone valve control) warm and normal, while others aren't?
So I don't buy the impedance argument, but have been known to be wrong :) I suspect that the extra cold weather (plus maybe the impedance) has revealed the need to replace the circulator motor.
I'm 1700 miles from my parents so I probably don't have all key information at hand and my father is having some problems processing too much info, and is somewhat spending-inhibited :)
But I suggested:
1. Re-check all zone valves to make sure they're open and working. (I assume this test will pass.)
2. Get a pro over to test the impedance/pressure in the system.
3. Replace or re-wire, and re-install the circulator pump (I suspect will be the issue).
Is it possible for the pro to determine by direct measurements on the system (i.e., without input about how the system *was* or *should have been* designed) how to fix the problem, or is it an issue of trying several alternatives?
Any other suggestions/remarks? (By the way: useful stuff at http://www.heatinghelp.com/ in newsletters.)
Many thanks!
--
D. M. Wood
snipped-for-privacy@comcast.net
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Smart man...

Ya think?

...go over the complete system, replace the incorrect parts, correct any other issues and schedule a tune-up!
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Your father's right.
wrote:

--
There are three stages to sex in a
person\'s life: Tri Weekly, Try Weekly,
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Ya......I can just see the gales of laughter when THIS fucking call comes in.
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wrote:

What? You dont have an impedence tester for hot water systems? Why I was just doing this yesterday .....................with my "flux capacitor". :-)
Bubba
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I use a flow meter..
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