Worcester Bosch Heatslave 18/25 External Oil

[Ben Browne]

Hello, we've had an ongoing problem with the hot water. Initially it'll run hot say for 2 or 3 minutes then it loses heat becoming barely warm. Funny thing is if you restrict the flow (we have a shower head connected to the the bath) it'll stay piping hot. Bath takes an hour to fill!!
Our plumber has replaced the hot water control thermostat but that has made no difference.
Any ideas would be welcomed.

 

[oilhead]

Symptoms of a scaled up domestic hot water heat exchanger.

 

[Ben Browne]

Thanks Oilhead.
Is it possible to descale/clean heat exchanger?

 

[Terrywookfit]

Yes. Needs removing though.

 

[Ben Browne]

Thanks Terry.
There has been an audible bang/thump coming from pipe work close to boiler when hot water is drawn....is that a failing heat exchanger symptom?

Easy enough to remove/clean/replace heat exchanger?

 

[Terrywookfit]

Is there any flow to rads when heating is off but there is water demand .?

 

[Ben Browne]

No rads are cold when heating off and draw on hot water although Ive noticed when heating is on and there is a significant hot water draw (ie running a bath) the rads go cool.

 

[oilhead]

No rads are cold when heating off and draw on hot water although Ive noticed when heating is on and there is a significant hot water draw (ie running a bath) the rads go cool.

That is what happens with combi's. it is in the inherent design; priority to hot water.