Remeha Avanta 24S CH fails to start intermittently.

[gerardo]

We have had this system boiler since February.

I have have previously replaced a Sunvic wired thermostat with a wireless Salus, well two infact, as I belived they had failed. Both indicated power at the receiver, the relay clicked but the boiler did not fire. The timer has been set to "on" for power to the receiver.

Assuming that the Salus had failed completely, I put the Sunvic back and the boiler restarted. Decided to replace the Sunvic with the Honeywell CM927 this weekend and took some advice here.

Unfortunately, the same problem has started with the Sunvic. The thermostat is clicking to call for heat but the boiler sits in standby with only 1 power LED instead of 2.

How or why it actually restarts beats me; I can shut down power and repeatedly on/off the stat but the boiler will eventually fire in its own time.
The longest known spell was on Saturday, when I returned the Sunvic to use.

For info the boiler is a system boiler. On previous occassions when this has happened I have turned the cylinder stat up and the boiler fires and turns off when turned down.

It seems as if the boiler is not getting switched or is locking off for some reason. I am unsure of the frequency of this but it has happened last night and Saturday.

As the boiler is less than a year old, I will discuss with the installer but am concerned that is intermittent. I take it I will have to test some voltages and note how the boiler panel is wired.

 

[gas4you]

What's the system pressure reading?

 

[rojaca]

may not be the stat at all. Programmer, wiring, or most commonly the zone valves.
I would look at your valves first.

 

[gerardo]

Does the zone valve return a signal to fire the boiler? So if the zone valve sticks, the stat will be on but the signal not getting to the boiler?

 

[Boilerman2]

Correct the Valves operate at the dictates of the Cylinder stat and Room stat and once open an auxillary switch in the motorised valve sends a signal to the boiler to fire up (see Broag Remeha Power wiring guide Page 6 wiring option 3 for S plan or Page 4 option1 for Y plan) as you will see the motorised valves will send a signal to Terminal 1 on X2 on the boiler PCB

 

[gerardo]

Thanks, briefly looked at the schematics today. So if it fails intermittently, would a replacement zone valve be a reasonable starting point or is there some maintenance to be performed?

 

[Boilerman2]

I think it is time to get the installer back as it is less than 12 months old he should be more than happy to come back and sort it!

 

[gerardo]

Totally agree but not had a return call yet.
If looking at a valve then will probably be at my expense. Just had a thumbs up for a guy my mate knows.... Relliable, knows his stuff etc so may make a clean break.