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Discuss Automatic bypass and radiator thermostatic valves in the Plumbing Forum | Plumbing Advice area at PlumbersForums.net

Messages
79
Hi

If the radiator valves are not demanding much heat and are near closed then the automatic bypass should be cutting in.

I have a few queries that may be obvious but not to me as old system did not have an automatic bypass.

[1] When it comes in it is shunting some of the hot water, will this not mean that the zones that do want a bit of heat are robbed of it?
[2] When it comes in and it starts to get hot (shunting the water) will the boiler not see a higher return temperature and think it needs less heat (or stops the burner) again meaning no heat for the near closed valves that require some heat?
[3] When it does cut in, how hot is it supposed to get?
[4] When it does come in then it seems noisy as the water is gushing through it - is this normal?

At the moment I have set it high and using open radiator instead (but that will be upping the gas costs so I would like to get the bypass working correctly).

Thanks
Colin
 
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king of pipes

Esteemed
Plumber
Gas Engineer
Messages
5,153
These type of systems are difficult to configure Mr Evil is more experienced and has the benefit of fitting it and having it installed, I would be guided by him there is such a low kw demand at times with evo home, modern boilers which have a low water content and move the system water quickly struggle to get going as there's no where for it to go, even when the auto bypass kicks in it doesn't drop the temperature it's like driving your car in 1st gear at 5mph , I very much doubt Worcester will be any help they would be guiding you to use their controls and weather compensation which in my experience is the way to go .
 

oz-plumber

Esteemed
Plumber
Messages
2,958
What boiler do you have?
Condensing or standard efficiency.

Condensing boilers have a much greater turn down ration than standard efficiency boiler.
 
Messages
79
System boiler ?? Where's your pump ?
Hi

I am not sure what you are asking, the boiler (from the installation and maintenance instructions) is a 30KW Greenstar 8000 Life gas fired condensing system boiler.

As far as I know there is no pump other than that built into the boiler (or if there is one external I cannot see/find it).

Thanks
Colin
 
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king of pipes

Esteemed
Plumber
Gas Engineer
Messages
5,153
I just needed to confirm you had a system boiler with a internal pump.
1 - your boiler is a range rated appliance meaning when it leaves the factory it set to full rate , when it was installed did the engineer adjust the heat output and pump curve to suit you system ? If not then your boiler will be Operating at Full rate the pump will be running at 400 mbar constant as the chart below.
2 - I recommend you reduce the kw output to 15 kw and pump curve to 2.0m of head as a starting point and monitor it's performance increase this gradually over the winter heating period if needed.
3 - reducing the output will save on gas , a lower pump head speed will quieten the system and take the pressure off the boilers internal components and reduce wear and tear.
Please study the attached tables below which are taken from your Installation manual and talk to your installer to see if adjustments have been made ? .

Regards kop
 

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Messages
79
I just needed to confirm you had a system boiler with a internal pump.
1 - your boiler is a range rated appliance meaning when it leaves the factory it set to full rate , when it was installed did the engineer adjust the heat output and pump curve to suit you system ? If not then your boiler will be Operating at Full rate the pump will be running at 400 mbar constant as the chart below.
2 - I recommend you reduce the kw output to 15 kw and pump curve to 2.0m of head as a starting point and monitor it's performance increase this gradually over the winter heating period if needed.
3 - reducing the output will save on gas , a lower pump head speed will quieten the system and take the pressure off the boilers internal components and reduce wear and tear.
Please study the attached tables below which are taken from your Installation manual and talk to your installer to see if adjustments have been made ? .

Regards kop
Hi

Thanks for the reply and advice.

The default for the boiler is constant pressure 250mbar (3-d1) and the default min output (5-A3) is 10% (this has had to be increased to 20% to work correctly with the control system I have).

The house will need access to at least 25KW if all radiators fully on and open, even more if hot water for cylinder comes on at same time. The boiler starts at the lowest output (20% of 30 => 6KW) and remains there for quite a while before bumping up its modulation - slow start mechanism)

I am not sure where the setting for 2.0 m of head is in the manual.

Thanks
Colin
 

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king of pipes

Esteemed
Plumber
Gas Engineer
Messages
5,153
Think 25 kw is to high , time your hot water heat up at different times to your heating , your rads will not be calling for full heat that often what's the minimum night time set back temperature. I don't advise lower than 12°c it better to be on a bit longer at a lower rate
Kop
 

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Messages
79
Think 25 kw is to high , time your hot water heat up at different times to your heating , your rads will not be calling for full heat that often what's the minimum night time set back temperature. I don't advise lower than 12°c it better to be on a bit longer at a lower rate
Kop
Hi

The min temperature is 16 degrees

Thanks
Colin
 

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