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Discuss Boiler and heating question in the Renewable Energy area at PlumbersForums.net

Jeffs123

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2
Hi,

I have a question about my s plan heating. I have a Worcester 35cdi erp boiler connected to 2 heating loops and an unvented indirect cylinder via 3 switch values. If I have the radiator heating on and water heating on the system doesn’t close the heating or water switch values. So doesn’t appear to prioritise. The flow temp on the system seems to all be from the boiler radiator control as the water one does nothing. I have 2 questions 1- can I have the setup changed to be able to use the water flow temp control on boiler for cylinder flow temp and the radiator control for heating flow temp as it is hardly ever in condensing mode as the cyclinder needs a high flow temp. How would this be achieved.
My second question is under the boiler I appear to have a loop from the heating flow back into the return with a red value on it. It’s hot after the valve so I assume some of the heating flow is going back into the return which causing the boiler to cycle as it’s hot (I think it does anyway) . It’s the one with a red arrow on the photo. What is the loop there for and should it be increasing the return temp? Any advice would be appreciated?
 

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Jeffs123

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Thanks for the response I appreciate it. The integral diverter looks like it would do what I needed for separating the flow temp for CH and water. I’ll have to get a quote from someone. I’m still perplexed by the bypass valve though. It appears to be on 6, but when I open the switch valve for heating water (cylinder)and the boiler radiator temp control is set to 60, but the copper pipe is only 51.7 on the main flow out and the pipe after the bypass valve is 50, so this implies it’s going through the valve even with the loop open. The return from the cylinder is only 43C prior to the bypass pipe joining/connecting to it. I have a few questions
1 The flow out seems low at 51.7 when the digital display on boiler says 60 is this due to the high return temp?
2 Should the bypass even be allowing heated water through, as the cylinder valve is open?
3 if this bypass return is almost as high as the main flow, then will the boiler just cycle all the time?

Once the pipes have cooled I’m going to open both heating loops as well and see if the return heats up with those valves open. Surely with both CH loops open the bypass shouldn’t heat up. Also when I look at S plan systems they all seem to have a pump on the circuit for CH. My system doesn’t it does have a pump on the cylinder, but I was told this is just for instant hot water at the tap, we have this off though. Will the boiler pump be sufficient as its a relatively large house 4 bed, 3 bathrooms 10 rads up stairs, 7 downstairs.
I think I’m going to need someone to come out. If I joined British Gas service scheme would they check all these things and fix them? I’m no central heating engineer, but something seems wrong to me.


Edited: I tested the system with both CH loops calling for heat… both values open and the bypass still gets hot, so something is wrong
 

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Last edited:

ShaunCorbs

Staff member
S. Mod
Plumber
Gas Engineer
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31,780
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2
The boiler is reading heat exchanger temp

No the bypass shouldn’t be opening unless all zones are closed

Yes or the full heat isn’t going to the load eg cylinder or rads etc

Pump is in the boiler the one on the cylinder is a bronze secondary return pump

I wouldn’t go bg a decent heating engineer is better than bg
 

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