Calling all Vaillant men

[bodlamby]

Hello Guys,
I have a ten year old Vaillant TurboMAX pro28 and have the following problem:
The ignition indicator flashes at very intermittent times. (showing lack of water or poor circulation)
On CH it could happen three or four times in one evening and then not happen for the next two days. If the CH is working at the time and I call for HW then the indicator will flash and the system will stop. If I switch the CH off and call for HW then the system runs okay. This suggests to me that the pump may be on it's way out as it can sometimes cope with the CH system load (and sometimes can't) but on HW only, it manages with just the boiler load (only the 'weight' of the water in the boiler).

System checks and remedies carried out so far:
I have flushed out the system.
Replaced the diverter valve in September with genuine Vaillant spare.
These two remedies seemed to clear the problem for about six weeks before it came back.

What I am finding hard to understand is how this fault could occur so intermittently. How does the boiler work out low flow when there is no flow meter in the CH system. Does it use the NTC sensors to check the temp differential between flow and return to gauge some sort of flow rate. I would be interested to know how it does it.

I am currently considering the options below.
1. Replace NTC sensors
2. Replace pump
3. replace electronics board.

Any help from you chaps would be very much appreciated.

 

[Agile]

I am sure if you replaced those four parts there is a possibility that it might solve the problem.

But if it was me then I would be calling a boiler engineer to diagnose the problem both to avoid changing expensive parts and in case it was something very simple.

Depending on where I lived then I would be looking for someone called Tim.

 

[mysteryman]

Poor flow can be deduced from a too-rapid temperature rise. It is not likely to be faulty sensors. Check the rate of temperature rise when it fires up. If it is more than about one degree per minute, it is excessive, and you should look to the pump, airlocks or sludge.