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Andrew Smith
Andrew Smith, Engineer
Category: UK Plumbing
Satisfied Customers: 2814
Experience:  Domestic Gas, Commercial Gas, LPG, Unvented Hot Water, Part P Electrical, Commercial Catering
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My Boiler will not fire up the central heating even when i

Customer Question

My Boiler will not fire up the central heating even when i put my room thermostat to full, however boiler fires up for water heating no problems, originally thought was 3 position valve so changed to new one.
Submitted: 2 years ago.
Category: UK Plumbing
Expert:  Andrew Smith replied 2 years ago.
Hi my name is XXXXXX - lets see if we can get you sorted in the shortest possible time. Can you let me know the make and model of the boiler?
Customer: replied 2 years ago.

Boiler is Glowworm 15HXI

Control Panel Sunvic SP2

Thermostat ( room) Sunvic PLX

Have just replaced Sunvic 2701 3 pos valve

Expert:  Andrew Smith replied 2 years ago.
What happens when you have both the hot water and heating on and then turn off the hot water at the clock?
Customer: replied 2 years ago.

the boiler stops operating

have turned heating off on controller and water on and the boiler works fine.

but turning water off and heating on and room thermostat to full the boiler will not fire up.

you can hear the thermostat click!when on full

Expert:  Andrew Smith replied 2 years ago.
Can you tell me what happens when you have the hot water and heating on and then turn the hot water off at the cylinder thermostat?
Customer: replied 2 years ago.
wont be able to do that until later tonight as i am in work now, however from what i have learnt already the cylinder stat has no on/off just a dial that seems to go round and round with no definable stop on it
Expert:  Andrew Smith replied 2 years ago.
OK, you need to replace that. The power for the 3 port goes through that also, so when your hot water is satisfied and turns off it is supposed to send a signal back to the 3 port.
Customer: replied 2 years ago.
ok will try that
Expert:  Andrew Smith replied 2 years ago.
Let me know how you get on.
Customer: replied 2 years ago.
Thank you i will
Expert:  Andrew Smith replied 2 years ago.
No problem
Customer: replied 2 years ago.
Changed cylinder stat, checked new one working ok, turned cylinder stat to off position , central heating will still not fire up
Expert:  Andrew Smith replied 2 years ago.
Central heating will not fire up when on at the clock and room thermostat and the hot water off - it is either a problem with the clock, the room thermostat (as this is where the power comes from) or the wiring to the 3 port valve. Do you have a diagram to check it against?
Customer: replied 2 years ago.

checked wiring then double checked all seems as it should be,

im not sure how to check room thermostat for power to 3 pos valve

or control panel for +ve feed

Expert:  Andrew Smith replied 2 years ago.
Room stat should be live on 1 and then out on 3;
http://www.honeywelluk.com/Documents/All/pdf/940.pdf
If you get stuck I can talk you through this wire by wire.
Customer: replied 2 years ago.
live as in 240 v
Expert:  Andrew Smith replied 2 years ago.
When you turn the thermostat up do you get power back down 3. Did you get the diagram OK?
Customer: replied 2 years ago.

got diagram thank you unable to check until this evening due to work commitments, why does work always get in the way!,

you are not required to answer the last question by the way

Expert:  Andrew Smith replied 2 years ago.
Just drop me a line when you get round to it.
Customer: replied 2 years ago.

Andrew

good morning

having now tested my system and checking wiring is same as PDF this is what i have found

when cylinder stat is calling i have 235v going to orange wire of 3 way valve

and 168v going to grey of 3 way valve.

when cylinder stat satisfied or off i have 235v to grey wire and 0 v to orange wire.

 

when CH calling i have 237v to white of 3 way valve

and 236v to grey of valve.

when CH satisfied or off i have 40v to white of valve.

the plot thickens

Expert:  Andrew Smith replied 2 years ago.
The 168V - ish is usual when the valve is sat in some positions. I will look into this deeper.

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