Vaillant Turbomax VUW 282 E Heating problem

[Dalk]

I hope someone can please help me out with the problem below.

I have a 10 year old Vaillant 282 Turbomax boiler and recently due to problems changed the following:

1. main heat exchanger
2. Pump
3. Serviced Diverter valve with Vaillant service kit

The DHW works fine but the heating is 'overheating' to specified temperature within minutes. I have set the front dial to 6.5 and when the heating turns on the temperature gauge shoots up to this temperature setting in about 2 minutes. Then the boiler runs for about 10 mins. After that it cycles 'on' and 'off' but for short duration only. Although i still manage to get the house warmed up there is obviously something wrong.

I changed the temperature sensor but that did not make any difference.

I am suspecting either the control board or maybe Differential pressure switch ?

Any help greatly appreciated.

 

[davebgas]

why did you have to change the main heat exchanger and pump? What were these 'problems'???

 

[Dalk]

The main heat exchanger was blocked up. The heating would not work thus i thought that the pump was faulty since i had already serviced the diverter valve. Then when i started to check out the main heat exchanger i realised it needed replacing.

 

[davebgas]

Have you checked the pump again? if its carped up then i'd be sniffing around in that general area

 

[Dalk]

i have taken off the pump a couple of times and seems clean enough.

however i have put sentinel sludge remover to clean the system out. i took most of the radiators off and flushed them but some were difficult to acces so thus i put sentinel in system. But i suspect problem within boiler and not external.

 

[davebgas]

Still seems definately something to do with circulation rather than the electronics. I know the pump looks clean, but is it working????

 

[gas4you]

Are you sure you re-assembled the DV correctly? Could be it is stuck in HW position.

 

[Dalk]

I do hope that it is circulation and not electronics!
This is not the first time that i serviced the DV. But that does not mean i cannot make a mistake. I have since taken it apart and re-checked. Can't see anything wrong ?

Davebgas are you implying that the pump could be partially working ? If so whats the best way to check/clean ?

Thanks

 

[davebgas]

does the return pipe get hot when the system rapidly heats up?, and when i say heats up, i mean to the temp of the flow?

 

[Dalk]

Yes it does but not to the same temp as the flow. Thus the reason to flush radiators and use sentinel anti sludge. This radiator flushing has made an improvement to the heating and i did not suspect a blockage causing the boiler to overheat.

 

[gas4you]

If it was the pump I would expect the dhw not to be working either and the boiler going to overheat then as well.

 

[Dalk]

I would tend to agree with you gas4you. Of course the CH circuit has to be first eliminated as being a problem. The sentinel cleaner can take up to 4 weeks to work and it's only been about 2 weeks yet. Once the flow and return pipes achieve the same temp then i am hoping that the boiler temp stabilises.

Now, i had no issues with either overheating or faulty electronics prior to the problems starting. But i thought changing the main H exchanger and cleaning the secondary one and servicing the DV would have fixed it. But obviously the CH circuit is affecting the temp. But is this the whole problem ?

Also, the temp reading on the gauge is sent by the connection to the overheat thermostat. The NTC reading goes to the main pcb and controls the fan. Would i be right in still assuming problem is blockage related?

I have also cleaned out the diferrential valve. Diaphragm looks a bit worn out but the lever actuates ok. What are the symptoms if this is faulty ?

Thanks to all.