Hot water issue

[Buster boiler]

I have a ferroli combi 77 ff boiler ,when you turn the hot water tap on it gives hot water at first then goes cold,central heating works fine, can one of you maestros please give the answer

 

[polesapart]

Bithermic heat exchanger? I'd be looking at the flow switch.

 

[ianmcd]

faulty cold water flow switch

 

[Buster boiler]

Hi changed flow switch still the same scenario anymore suggestions will be appreciated

 

[CBW]

Does it actually fire up for hot water demand?

 

[Buster boiler]

Yes it fires up for 30 seconds then goes cold c/h is working fine

 

[Madrab]

The boiler fires up for 30 secs then it shuts off? What outlet are you running, a shower perhaps? Does it go off and then on again and repeats?

 

[Gasguru]

Does it repeat the cycle of hot/cold with the tap open?

 

[Buster boiler]

Sometimes it repeats

 

[ianmcd]

Could be a flue/fan problem, you cant check this yourself unfortunately

 

[Gasguru]

Indeed...could be fan/flue related and AFAIR these are positive pressure chamber boilers...registered gas eng. required.

 

[Buster boiler]

The outlet is just from the taps and repeats

 

[dilalio]

DHW requires full rate and boiler isn't happy at full rate so... You need an RGI!