WTF is with these radiators??

Hi Everyone ~
Big iron FHW radiators in an old colonial in Mass. Oil burner in the basement, just tuned up and checked last week. At the end of last season, one of the upstairs radiator and one of the downstairs radiators were slow to get hot for the 1st time in 7 years, which I tell the service guy.
Serviceman checks them, they are bled and all the valves are open wide. System is working fine as far as he can tell, but they are still slow to get hot - he thinks the zone around the thermo is getting hot too fast to allow the system time to reach the offending radiators.
That seems strange, as they were fine for the past 7 years.
Any thoughts? Things to check?
Thanks,
Bluesman
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Bluesman wrote:

Well, if he's right, then partially closing the valves on the radiator(s)
nearest the thermostat should fix the problem.
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wrote:

Hot water radiator valves need to be either all the way on or completely off. Partially closing them does nothing.
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Well, admittedly, I was thinking about steam radiators, having keyed on "big iron", instead of FWH, but unless the radiators in question are either hooked up serially with no bypasses, or driven by separate pumps, I can't see why it wouldn't work, anyway. Are you thinking of solonoid-driven valves, which don't really HAVE a partially closed state, or is there something about the dynamics of a typical HWH system that causes them to ignore flow restrictions?
--Goedjn
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SNIP

If you have the cast iron heaters fed by black iron pipe, your heaters may have resticted flow through them due to build up and corrosion. I was working on a site where, when commissioning the HVAC controls system, we had to verify each hot water heater operation. A number of them I could feel the top half of the heater supply pipe get hot before the bottom half of the same pipe did. The plumbing contractor removed one heater where we found that the bottom half of the heatrer was filled with "sludge". The heater had been in service for nearly 20+ years.
Something to look for. Contech
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