Strange Behaviour - Combi boiler

[opacey]

Hi all. My gas combi boiler (Worcester Bosch 30CDi) feeds radiators in each room of my flat. As far as I understand it the boiler should only heat water (central heating water, I mean) when the electronic line from the thermostat is switched on, or in other words, calling for heat. This should be true regardless of the closed or opened state of any of the radiator valves. I have noticed however that my boiler fires up whenever I open a radiator valve even if the thermostat is set to zero and isn't calling for heat (I have tested the terminals with a multimeter so I know the 'stat is working correctly). The CH side of the boiler appears to function like the HW side, i.e. whenever a hot tap in the house is opened the boiler will heat the flowing water up.

I called the Worcester Bosch support line and they think this behaviour is impossible. Other than this the boiler functions perfectly and is only a few years old so I don't think it is faulty. Before I call out a plumber, does anyone have any ideas or experience with this? Perhaps it is configuration issue.

Many thanks

 

[dcawkwell]

What does the pressure in the central heating system read on the boiler when you have the valve shut and when you open the valve.
Do you hear any flow of water at the boiler when moving the radiator valve.

 

[Dan Robinson]

Do the rad valves have a digital display?

 

[TCCHeating]

Press and hold the eco button on the boiler until it lights up green.

Does this solve the problem??

 

[opacey]

Pressure reading: It rest just under 1.5 bar and doesn't seem to change when I open any of the valves. I can't detect any sound of flowing water at the boiler when opening and closing that valves. I tried various combinations of valves.

Digital display on valves: In fact the control system is made by Heatmiser, something like those used for underfloor heating. Each room has a digital thermostat on the wall which is linked up to a central wiring box that then routes signals out to wax valves on each of the radiators. I've used a multimeter thoroughly all over the electronics and verified that it is working perfectly so I know that isn't causing the problem.

Eco setting: Boiler is always in Eco mode. NB, I don't believe there is a bypass in my CH plumbing apart from the one built in to the boiler itself.

Does any of that info give you a further hint? I'm still very surprised that the boiler chooses to fire up just when the CH water is permitted to flow by a valve (even when I open a valve with just my hand).

 

[opacey]

Okay figured it out.

The boiler comes factory set-up with a hard link between LS and LR on the PCB. ie, it is ready to fire up the burner when flow is detected. The wire from my thermostat system wasn't attached anywhere, it was loose inside the boiler. I have now attached that wire to LS and LR in place of the linking block and the system is working as it always should have (only heating up when the 'stats ask for heat).

I'm surprised to have heard from the manufacturer that the auto-firing behaviour I described isn't possible, it is apparently factory default behaviour. Another way of putting it is that the boiler is trying to fire up all the time but when all the rads are closed and there is no flow the safety shut off suppresses the burner.

I found this out with the help of a qualified plumber, I hope the information can help other people but please don't attempt anything you are no qualified to do.