vokera mynute error condition

[oldterry2]

I had a boiler changed a few months ago and it is intermittently showing an error condition. The new boiler is a vokera mynute 20VHE and it replaced a potterton netaheat 16/22 in the existing system (a Honeywell Y) and nothing else was changed. It all seems to work fine BUT occasionally the boiler stops showing a fault code 74 (no water circulation). After a reset it then all works fine until the next time.

So, has anyone seen this, or does anyone know what is likely to be causing this (and how to fix it , if it isn't a boiler fault)?

Also does anyone know what mechanism the boiler is using to decide there is no circulation?

 

[Agile]

Has the system been converted to a sealed system?

Tony

 

[oldterry2]

No, it is still an open vent system (that's why its a VHE boiler)

 

[Groovejet]

Check ye Pump. You said it was a Y plan? Could have intermittent fault.

 

[Groovejet]

Also flow sensor

 

[Agile]

As stated check the pump. Ideally with the finger test as described in the FAQ on this site.

Where possible I always convert to a sealed system. OV systems are much more susceptible to air being sucked in and that can give rise to those kind of faults.

I am not sure how yours monitors flow but most compare the temperature difference between flow and return and iff too high concludes there is a lack of water flow.

Do you have TRVs on all rads and no bypass?

Tony

 

[oldterry2]

As stated check the pump. Ideally with the finger test as described in the FAQ on this site.
Do you have TRVs on all rads and no bypass?

The pump has always been working when I've looked at it .
There is one radiator without a TRV to act as a bypass.

 

[Agile]

You dont check a "pump" just by looking at it!

Has it even been bled?

What speed setting is it on?

Tony

 

[oldterry2]

You dont check a "pump" just by looking at it!
Has it even been bled?
What speed setting is it on?
Tony

I was using the term 'look' as a shorthand for investigate/examine, and I do know how to tell if an electric motor and its associated pump is running. The complication, of course, is that the pump is powered via the boiler so the pump power is dropped when the boiler decides there is a fault. So far whenever the boiler has been reset and power restored to the pump, the pump has been working. (I hate rare intermittent faults).

Yes, the pump has been bled.

The fault has occurred on both mid and high settings. I've even tried it on low speed to see if I could provoke the fault (so naturally the fault did not occur!).

 

[picasso]

is the pump connected directly to the boiler? if its connected via a wiring centre the pump overrun wont function and will give the symptoms you got, the VHE is an open vent boiler as I am sure you know and its not suitable for sealed systems, dont know why but vokera wont allow it.

 

[Agile]

Vokera are either lacking in confidence or the boiler does not have an overheat stat which cuts the supply to the gas valve.

On an OV boiler if it overheats, then the water just harmlessly boils away.

With a sealed system it will boil the water and cause the system to explode.

Tony

 

[oldterry2]

is the pump connected directly to the boiler? if its connected via a wiring centre the pump overrun wont function and will give the symptoms you got.

The pump is connected to the boiler, and the pump overrun does occur.

(sorry for the delay in replying, been away from home.)

 

[steved101]

Does the pump have a permanent live connection to it..... new system wired up correctly? As with a pump overrun the wiring is slightly different

Run the boiler - after about 5-10 mins turn the stat to off - see if the pump still continues to run

 

[oldterry2]

Does the pump have a permanent live connection to it..... new system wired up correctly? As with a pump overrun the wiring is slightly different

Run the boiler - after about 5-10 mins turn the stat to off - see if the pump still continues to run

No the pump does not have a permanent live feed - it gets its live supply from the boiler. The pump does continue to run after the demand ceases.

I did check that the pump was wired up correctly; that was the first thing I thought of as being a possible cause.

Cheers

 

[oldterry2]

an update:
Vokera have been in and looked at the boiler, and have swapped out both the thermistors. The engineer said that when they get an intermittent fault, those are the first things they replace and normally that fixes things. I also got him to undo and remake all the connections to the master logic board.