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 Post subject: New Radiator problem
PostPosted: Mon Oct 15, 2018 8:04 pm 
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We have recently installed a new kitchen with a brand new radiator. When switching CH on constant the radiator heats up nicely pretty soon. However when we put it on a timer, overnight or at work etc, it only gets luke warm.

I have bled it..checked the outlet valve and the TRV seems to be fine(pin popping up and down).
So it seems to be an issue with having heating on manually or on a timer. All other radiators fine.

Any help would be appreciated!


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 Post subject: Re: New Radiator problem
PostPosted: Tue Oct 16, 2018 10:25 am 
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I don't see how it can be caused by the timer. All the timer does is say when the boiler can be turned on and off. The actual turning on and off is controlled by a thermostat, usually in the hall.

I assume "overnight or at work" means you have the timer set for a schedule similar to this: ON at 0600; OFF at 0800; ON at 1700; OFF at 2200. The heating is then off between 0800 and 1700 when you are at work; and between 2200 and 0600 when you are asleep.

How soon after the heating is turned on are you checking the radiator?
What happens if you remove the TRV head?
Were all the radiators rebalanced after the new one was fitted in the kitchen?
Have you checked if the room thermostat is still calling for heat?


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 Post subject: Re: New Radiator problem
PostPosted: Tue Oct 16, 2018 4:55 pm 
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:welcomeuhm:
As per D Hailsham, chances are the rad coming on on timer it gets just as hot as when you switch on manually, most of us set the timer for before we get up or before we get in from work it's just that once the house is up to temperature the rad cools somewhat...

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 Post subject: Re: New Radiator problem
PostPosted: Tue Oct 16, 2018 7:48 pm 
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Thanks all for reply.

We have not had them balanced and maybe that is needed. My apologies for a bit of confusion as well. Last night I set timer to come for heating only on at 5am and when up at 6.30 the radiator was lovely and warm.

The issue seems to be when I set the water AND heating to come on together. Heating only=hot. Heating and Water=luke warm.

All other radiators hot either way.

Cheers


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 Post subject: Re: New Radiator problem
PostPosted: Wed Oct 17, 2018 2:28 am 
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Had this with sons house, leave the central heating running all radiators fine, turn it off and back on again they took ages to warm up again. The problem was the lock shield valves, they were all wide open, so on start up, instead of water going through every radiator, what happened is it went through the easiest one, then the returning hot water modulated (turned down) the boiler, as the room heated up, then the TRV would close, so water then forced through next radiator, again as that room warmed up the TRV would close and so on, once all rooms warm the TRV's would open and close keeping all rooms warm, it was only when first switched on there was a problem.

Cure was easy, turn off the lock shield valves in every room then turn back on 1/2 turn at a time, found his needed about 2.5 turns to allow water to start flowing, once done then whole house heated up together, and boiler did not modulate until rooms were warm.


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 Post subject: Re: New Radiator problem
PostPosted: Wed Oct 17, 2018 12:29 pm 
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Sheedsn wrote:
The issue seems to be when I set the water AND heating to come on together. Heating only=hot. Heating and Water=luke warm.

Set the hot water to come on 30 minutes to one hour before the heating. The cylinder should then be upt temperature before the heating turns on. With a modern well-insulated cylinder you can heat it up at midnight and the water is still hot in the morning.


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 Post subject: Re: New Radiator problem
PostPosted: Wed Oct 17, 2018 1:30 pm 
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ericmark wrote:
Cure was easy, turn off the lock shield valves in every room then turn back on 1/2 turn at a time, found his needed about 2.5 turns to allow water to start flowing, once done then whole house heated up together, and boiler did not modulate until rooms were warm.

Even half a turn open can be too much - depending on the temperature drop across the rad; and most lockshield valves are fully open by 1.5 turns.

The flow rate through an individual radiator is very small compared to the capacity of the pipe feeding it, so the LS valve has to be shut down a lot to give the correct flow. For example:

A 15mm pipe can carry 6kW (at 11C differential). So if you are feeding a 1kW rad you only need 1/6th of the flow. With a 20C differential you will only need about 1/12th of the flow.

Adjusting a LS valve in 1/2 turn bites is much to much. Start with all LS's set to 1/3 turn open, then make small (1/12 turn) adjustments.


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 Post subject: Re: New Radiator problem
PostPosted: Wed Oct 17, 2018 5:49 pm 
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In the real world I would not put more than 4Kw of heat onto 15mm pipe work.

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 Post subject: Re: New Radiator problem
PostPosted: Fri Oct 19, 2018 10:41 am 
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gas4you wrote:
In the real world I would not put more than 4Kw of heat onto 15mm pipe work.

That's very conservative (small c). I was assuming a velocity of 1 metre/sec; 4kW is 0.6 m/s. The maximum recommended is 1.5 m/s, which equals 10kW (all at 11C differential. If the velocity is too low sediment can collect in horizontal pipes and air entrainment does not occur.


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