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  1. #1
    Join Date
    Mar 2009
    Location
    Washington, DC
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    1

    Default Hot water baseboard heating issues

    Hi,

    We recently purchased a 1900's row house with hot water baseboard heating. The gas boiler is relatively new (home inspector said 2003 I think). It's a 2-zone system with one zone for the English basement and one for the 2 floors of the main house.

    First, the thermostat in the main zone does not appear to be working. It's the standard Honeywell "round" with mercury and even when turned all the way up, the boiler doesn't fire. The thermostat in the basement does appear to be working, however there is a 30 second to 1 minute delay between turning the thermostat up and when the boiler fires (same when turning it down). Is this normal? Every other place I have ever lived, when you adjust the thermostat, the heating system responds immediately. I'll be replacing the thermostats anyway, but I'm concerned that the wiring between the thermostats and the boiler may be defective.

    Secondly, when the boiler is running, it seems to shut off before the called-for temperature is reached. I'm guessing it's hitting some sort of auto-shutoff because the temperature gauge on the boiler is getting up to around 200. Is there some way to adjust this?

    Finally, a quick question. There's a shut-off valve that's labeled "boiler water supply". Common sense tells me this should be open, but when we had a plumber out for another issue, he told me it should be kept closed. Which is it?

    I appreciate any help. Thanks in advance,
    A.J.

  2. #2
    Join Date
    Feb 2008
    Posts
    555

    Default Re: Hot water baseboard heating issues

    amuldoon:

    Yes, it is normal for the heat to be delayed a minute or so after the t-stat is first turned up to call for heat---Under ordinary conditions, when you turn up the t-stat you are actually closing a little mercury switch inside the t-stat---this signal then goes to the zone valve for that particular zone to instruct it to open so hot water can flow thru that particular zone---it takes approx. 90 seconds for the little electric coil or motor inside the ZV to open the valve.

    Once the zone valve is instructed to be open there is a little end switch that closes contact and instructs the boiler via 2 wires to the TT (thermostat) terminals on the aquastat (located on the boiler) to fire the boiler and activate the circulator (pump) to start pumping hot water thru the zone requesting heat.

    This boiler firing & circulation will continue until the water reaches its HIGH LIMIT (usually of 180-200 degrees)---the HIGH LIMIT SWITCH inside the aquastat will shut off the burner flame & the circulator will continue to pump water thru the zone until the t-stat in that particular zone opens (is satisfied & no longer calls for heat) & the boiler shuts down---if the water temp falls below a certain value while circulating (differential switch) the differential inside the aquastat will fire the burner to keep the water between 160-180 until the t-stat is statisfied.

    Since the zone in the lower part of the house seems to be working flawlessly, the suspicion points to the zone valve for the upper floors---could you post back & advise what brand of zone valve & model # you have---also closely examine with a strong light the zone valve that doesn't seem to be working--turn off the boiler on/off switch temporarily while you're examining the components.

    Many zone valves have a little grille-work that you can see inside with a strong light to see any burned components, or even a melted housing when they go bad---also get your nose as close as you can to see if you can smell any burnt smells that may be present---have you noticed any unusual odors when you entered the boiler room since the boiler's been acting up???

    Also check that the wiring to the zone valve hasn't been disturbed--that all wiring connections to the screw terminals of the zone valve are tightly connected & not touching anything else---most zone valves have a little MANUAL LEVER on the side or bottom of the ZV to allow temporary manual operation, so that the zone is manually opened so that some heat is directed up the the upper floors when the lower zone t-stat calls for heat---this will give you some heat upstairs until you can diagnose the exact problem.

    Yes, the boiler water supply valve is usually left open in order to supply adequate water to the boiler in the event of a small leak---in any event, check the PSI needle on the boiler gauge---it should read approx. 12 psi when the boiler is cold & no more than 25 psi when the boiler is hot & producing heat---if the psi gauge reads near zero, it means that there is inadequate water in the boiler & some must be added to maintain a minimum 12 psi on the boiler gauge.

    I would not change the t-stats until the problem is solved---the "round" Honeywell mercury switch t-stats are ideal for your heating system because they are compatible---any new t-stat must have a heat anticipator setting of .9 to be compatible with most zone valves.

    If no problems are found in your initial examination, the next step is to make an EXACT DIAGRAM on a piece of paper of the wiring arrangement to the terminals of the zone valves (should be the same color coded wires on both zone valves going to the same terminals on the ZV)---once you have the diagram, the boiler on/off switch can be temporarily shut off, there is a 40V low voltage transformer that should also be disconnected at one side to kill power to the zone valves.

    The ZV POWER HEAD (the upper half of the ZV) can then be switched by twisting the upper portion that separates from the lower portion---there is no need to drain the system---replaced on each of the lower housings & rewired according to the diagram---if the switched ZV power heads now work with the upper zone working now & the lower zone not working now, the problem is in the zone valve that was originally suspect---power heads are widely available at plumbing/heating supply outlets for approx. $30-50.
    Last edited by NashuaTech; 03-31-2009 at 01:54 PM.

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