New Boiler


Postby Coins » Fri Mar 14, 2008 4:09 am

I've recently had a complete new system installed (Combi Boiler.) Although rads upstairs and bypass rad have been gagged in, the temp downstairs is struggling to get to 20deg even when it's been running for a couple off hours. The boiler is constantly on trying to achieve the temp. Am I right in thinking the system should heat up quick and only kick in every now and then to top up heat.
Hot Water is fine
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Postby htg engineer » Fri Mar 14, 2008 11:56 am

That's normally how it would work, once the desired temperature is met, the boiler will keep cycling on and off to maintain that temperature.

You have to take into consideration 'air changes' this is how many times doors are opened where the temperature could drop. If people are in and out all day, then downstairs will be cooler than a bedroom that's left with doors and windows closed.

Are the rooms downstairs large ?
correct size radiators fitted ?

Do you find upstairs gets too hot ? or much hotter than downstairs ?

Try balancing the system, turning down the upstairs radiators to see if this make any difference.

Does downstairs feel warm ? is the room thermostat in the best place ?
(i take it the room stat is what you're going off when you say it doesn't reach 20deg)
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Postby Coins » Fri Mar 14, 2008 8:49 pm

The upstair radiators have been turned down. The problem is the desired temperature is not being achieved. So far the stat(head height, living room) is set for 22deg and barely making 20deg with the heating on for a number of hrs. My main concern is it is roughly between 5-8 deg outside the house, surely during the winter months a comfortable temp inside the house would be near impossible as things stand just now.
Radiators seem properly sized. the boiler has an CH output of 24KW. For a 5 bed house is that adequate
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Postby ericmark » Sat Mar 15, 2008 12:50 am

My son had a similar problem. Then once it got hot all was OK. If he allowed it to switch off then ages to warm up again. It turned out it was due to lock shield valves not being set correctly and until the temperature was high enough for the TRV's to start working it was allowing hot water to return to the boiler which results in the output being reduced. Once the 15 deg drop was set on each radiator then all worked OK.
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Postby DONFRAMAC » Sat Mar 15, 2008 1:20 am

Your room-stat should not be in your main living-quarters, but more commonly in the hall, beside the programmer, and away from the hall rad., which is normally fitted with 2 isolator valves set wide-open. Fluctuating temperature in the hall usually makes the stat. cycle, and the thermostatic radiator valves you should have fitted to ALL other rads., allows living-quarters to reach the set temperatures.
Hall radiators are usually small and lose heat up a tall stair-well, to ensure cycling, and for that reason I set my top-landing radiator for a minor output;-- just enough to take the chill off unused bedrooms, which have their doors left open, and rads. valved off at their TRV's.
I have always chosen to run my CH & DHW on 24/7, even with my old Gloworm 40,000 BTu/hr vented boiler system (~ 12 KW). I now have a 28 KW Potterton HE+ condensing combi , also run 24/7.
The room-stat in the hall is set for 25 C, and TRV settings in the living-room of 4.8 on a scale of 0 to 6, achieves a steady temperature of 22 C at head-height when seated, and a hall temperature of 21 C.
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Postby gremlin_1 » Sun Mar 16, 2008 12:08 pm

1, How many rads in the property?

2, What sort of boiler do you have?
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Postby gremlin_1 » Sun Mar 16, 2008 12:12 pm

:oops:
Found your boiler size

[quote][i]Radiators seem properly sized. the boiler has an CH output of 24KW. For a 5 bed house is that adequate[/i][/quote]

24kw boiler not adequate for large family house
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