Thermostat-Pump Overrun

Hi All, After giving our elderly (17yrs old) Cental Heating system a much needed service/overhaul(boiler was flat out all the time whatever position the boiler stat was set to-so we got hotter as the night progressed) I was a bit surprised to find with a new boiler stat fitted that even on the lowest temp setting the house was still too warm 28-30 C.A friend in the trade suggested that as we had recently installed modern double-glazed windows and doors,we were finally getting the rooms warm without heating up all the draughts and cold air that used to be part of the house,the room temp was only now becoming apparent.We did not even have a room stat fitted,so fitting one would allow us to get a lower overall temp out of the system.The Glow Worm balanced-flue boiler only runs 6 rads,the H.W. taken care of by an incredibly reliable Corvec-Britony unit. So a room stat was fitted and a new wall-mounted timer as well(the old electric clock style unit fell apart while I was setting the time segments).We are clearly feeling the benefits from this relatively cheap upgrade but there is an issue with the original boiler wiring and thermostat overrun which I would like anyone in the NG to give any comments on,(my pal is in the Canaries,so I don't want to run up a massive phone bill for what is maybe an issue that is easily explained). The original pump wiring was not through the boiler stat/pump overrun but directly from the timer switch, so pump was running all the time boiler was on.I have wired the pump now through the new boiler stat/pump overrun - exactly how it shows in the original boiler service diagram.Is the pump overrun circuit designed to run on for a set time after each firing of the burner or only at a pre-arranged heat setting?I have only just finished the work and it seems that the pump only overruns when the system is quite hot.I am now not sure whether the original pump wiring was incorrect or was the pump running all the time actually intended?We also have always had the 1st rad in the circuit(small bedroom nearest to boiler) running seemingly hotter than all the others ever since moving into the house 15years ago,I wonder if again wiring the pump to "always on" was an attempt by the original installer to even the heat out in all the rads. OK men----------------any comments?
Many Thanks T.R.K.
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The boiler itself will decide when to use pump overrun. Some will always do it for a set period after firing. Some will overrun until their internal temperature goes down to a certain level. Sounds like you have a boiler that does this. In any case, this is much better than how it was before. Although before you have extra (unnecessary) overrun between firings, you will have had no overrun at all when the programmer turned the heating off.
Christian.
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The original pump wiring was not through the boiler stat/pump overrun but directly from the timer switch, so pump was running all the time boiler was on.I have wired the pump now through the new boiler stat/pump overrun - exactly how it shows in the original boiler service diagram.Is the pump overrun circuit designed to run on for a set time after each firing of the burner or only at a pre-arranged heat setting?
We also have always had the 1st rad in the circuit(small bedroom nearest to boiler) running seemingly hotter than all the others ever since moving into the house 15years ago,I wonder if again wiring the pump to "always on" was an attempt by the original installer to even the heat out in all the rads.
The pump overrun stat usually keeps the pump going until the boiler cools down to a pre-defined temperature.
Sounds like your system needs to be balanced in order to stop some rads from getting hotter than others. [Have a look at http://www.diyfaq.org.uk/plumbing/plumbingpage1.html#balancing in the FAQ for more details].
Roger
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This sounds like "shortcycling" to me - you may not be trucking the heat away from the boiler quickly enough, so the boiler stat turns off (to stop it blowing up), but the room stat is still demanding so the pump keeps running and circulating water.
I had a bad case of this due to oversized (more is better) boiler for me hovel, but managed by fitting a couple more rads and turning down the boiler - not a user control, allegedly, to make it pretty good.
In ay event, it's no more than an annoyance, and working as intended for safety, and if you have a serious power mismatch, may not be curable.
BTW, could you ask outlook express to word wrap to 75 characters or thereabouts, the end of your lines is outside my door.
Though good old Xnews does rewrap on for me, I don't know if other readers do
mike r
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