Ideal icos he24 boiler constant 'c' with banging noises

[Nat2000]

Hi All, Our Ideal icos he24 boiler display constantly shows 'c' and the reset does not work. It heats up the water and central heating. But makes loud banging sounds when the CH demand is turning off. Then shows HA over heat error code. After few minutes goes back to 'c' and repeats.
I think if it resets to go back to '0' when there is no demand then the problem will be solved.
My understanding is- when CH demand is off, the motorised valve closes, but the boiler is still on. This heats up the water in heat exchanger to boiling which causes banging noises as water has no where to go. This over heating leads to HA code.
I suspect it is the faulty control pcb which is stopping the reset to '0'. Pressure is set to 1bar after bleeding all radiators.
I am not an expert. Any thoughts about anything else that may be faulty? Your help will be appreciated. Thank you

 

[terryplumb]

Your motorised valve is faulty. Is it a mid position. ( 3 port ) valve ?

 

[Nat2000]

I believe, the motorised valve is 2 port. It is attached to a straight pipe. I believe it allows or stops the flow depending on whether there is demand or not

 

[terryplumb]

Quite so , I assume you have two of them and one is faulty.

 

[Nat2000]

I can see that the lever on one valve slides perfectly whereas one on other is kinda stuck at closed position. But this valve does open and close as we do get hot radiators when ON.
The banging sounds come only when demand is going off. I presume this is when valve should close, Isn't it?
Still don't know why boiler can't reset to '0' status.

 

[CBW]

Motorised valve could be on wrong way. Something is sending a switch live back by the sounds of it, but could be the microswitch is stuck, which is essentially what @terryplumb has suggested.

 

[Nat2000]

Looks like the motorised valve needs replacing.
Not sure why reset shouldn't work on the boiler though.

 

[ianmcd]

I suspect it is the faulty control pcb which is stopping the reset

Why does every DIYr think that changing the most expensive part on any boiler will cure everything, it is not the PCB

The reason it wont reset is the boiler is still too hot and the hi-limit thermostat is doing its job

one of the micro switches on one of the zone valves is sticking and your system has never been installed properly, you should have an automatic by-pass fitted

You will have at least two motorised valves not just one if it is a 2 port always best to post pics of everything

 

[Nat2000]

Thanks for your reply.
The boiler won't reset even when it is cold.
I have tried switching it off for 8 hours then turning it on, still it doesn't reset. It shows 3 then goes to 'c' and fires up even when there is absolutely no demand. It should have been in stand by showing '0' without firing up in this situation.
No matter what it won't reset. Hence it think it is the pcb. Do it make sense?
Also checked the motorised valves and pump, they seem to work fine with or without boiler on.

 

[terryplumb]

Have you got a multimeter that you can safely use to measure mains voltages ?

 

[CBW]

It shows 3 then goes to 'c' and fires up even when there is absolutely no demand. It should have been in stand by showing '0' without firing up in this situation.

If the microswitch is stuck, then there’s your demand irrespective of what the controls are stating.

 

[Nat2000]

Have you got a multimeter that you can safely use to measure mains voltages ?

Yes, I have a suitable multimeter. What voltages do I need to check.

 

[Nat2000]

If the microswitch is stuck, then there’s your demand irrespective of what the controls are stating.

Are you referring to the microswitch in the motorised valve? Does it dictate demand? I believed the thermostat does it. When the room temperature is less than required, it triggers the pump, the motorised valve and the boiler to go ON. The boiler then keeps firing up and off depending on its internal thermostat. Is this right?
When the required temperature is reached on room thermostat it turns off the pump and motorised valve and puts the boiler in standby. Is my understanding correct?

Update - You are right. My above understanding is wrong. When motorised valve is in position it triggers the pump and boiler. Thank you

 

[terryplumb]

Go to the wiring centre and show us a pic of wiring. You should identify the terminal that contains the orange wires from the motorised valves ( they would both be in the same terminal block as the switched live to the boiler). With all power off to heating system, and using multimeter to test for no voltages present ,remove them and put them into seperate insulated terminal blocks.
Put power back on and with programmer/ timer off ( no demand for heating or hot water) boiler shouldn't fire up now .
Then measure voltages Between orange wire and earth ,one of them will read 230/240 volts if it's microswitch is stuck closed circuit.

 

[Nat2000]

Go to the wiring centre and show us a pic of wiring. You should identify the terminal that contains the orange wires from the motorised valves ( they would both be in the same terminal block as the switched live to the boiler). With all power off to heating system, and using multimeter to test for no voltages present ,remove them and put them into seperate insulated terminal blocks.
Put power back on and with programmer/ timer off ( no demand for heating or hot water) boiler shouldn't fire up now .
Then measure voltages Between orange wire and earth ,one of them will read 230/240 volts if it's microswitch is stuck closed circuit.