Vitodens 100 water no heating enough

[coltmanneil]

Hi ,
This morning my DHW is not heating up very well although it is firing the boiler up so it is trying .
It gets serviced every year not flushed . Could this be my heat exchanger. Is the same HE used for both central heating and DHW ? The central heating is working fine the problem is just my DHW. It is trying to heat it is not cold and burner firing up.
It is a vitodens 100w wb1b 30kw.
It’s done well over 12 years.
My central heating is working great.

Thanks

 

[CBW]

Could be the Diverter valve, stepper motor, plate heat exchanger main heat exchanger. Try from cold running the hot water and feel the flow pipe and if it heats up you’ve potentially found your problem.

 

[coltmanneil]

Hi
So run cold first then switch to hot , feel hot water pipe from boiler ?
Thanks

 

[coltmanneil]

He’s some more information.
We tried the hot water from another position and it was heating up but then went cooler and tried to heat up again and then went cooler.
When I felt the hot water outlet from boiler it was hot so it is trying but is working intermittently. Could this be diverter valve or HE any other checks thanks .
Neil

 

[CBW]

No don’t feel the hot water pipe, feel the heating flow pipe (usually the larger left hand pipe) under the boiler. Also check to make sure nothing passing, try to isolate the cold feed into the boiler and run a hot tap, if you get running water, then this could also give the fault you describe.

 

[ianmcd]

If the CH pipe is not heating when you run HW as per @CBW then it sounds like you have cross over from a thermostatic shower or thermostatic mixer tap

 

[terryplumb]

Is it that when you run any hot tap the water runs hot/ cold/ hot/ cold repeatedly ? Or it doesn't run hot at all ?

 

[coltmanneil]

Hi , it’s trying to heat up and then drops off repeatedly.

 

[terryplumb]

Does that mean you do get hot water from tap and then goes cold,leaving tap running this then repeats constantly ?

 

[coltmanneil]

Yes

 

[terryplumb]

I would suspect your plate Hex is blocked.
Probably best to engage an engineer.

 

[coltmanneil]

Thanks there’s a CH firm attending tonight it’s a 12 year old viessman vitodens which has never had a problem in all that time ( we’ve done well ) it’s serviced every year but if it’s costly to replace the CH heat exchanger might be worth changing it the boiler not sure what you guys would advise .
Was good to get some tests and advice from you guys first to see if we could pin point the problem. I am a marine spark so not familiar with CH and boiler problems.
A quick question is there only one heat exchanger in a boiler ?

 

[terryplumb]

No ,the plate Hex is specifically for domestic hot water .

 

[coltmanneil]

Thanks for that