combi boiler

[minoka123]

hi
i have got a combi boiler works fine only one thing to get the hot tap in the bathroom and kitchen to run hot it needs to be turned on three quaters of the way otherwise its cold any ideas
cheers richard

 

[D_Hailsham]

i have got a combi boiler works fine only one thing to get the hot tap in the bathroom and kitchen to run hot it needs to be turned on three quaters of the way otherwise its cold any ideas?

Yes, the boiler output is too low for the flow rate from your tap.

Combi HW rates are quoted for a temperature rise of 35C. If your actual flow is more than this, the rise will be less.

Measure the flow rate, using a graduated bucket - most of them have litre marks on the inside. You need 2.5kW for every litre/min to get the 35C degree rise.

 

[ianniann]

I'm not sure about that. Do you mean it is completely cold until you turn the tap up to three quarters or more? And then OK? That implies a flow sensor problem. Maybe badly adjusted, maybe sticking a bit.

Or just warm when the water is full on, but hot when it is three quarters or less? That would seem like an underpowered boiler.

 

[Gasman77]

id say its a worn diaphragm not turning the boiler on ubtil you have a good flow, i.e. opening the tap 3/4. if you open it fully i take it its ok?

 

[minoka123]

thanks for the reply the water is cold untill the tap has been three quaters of the way

 

[minoka123]

yeah the tap works fine when its on three quaters of the way

 

[D_Hailsham]

I've read your question again and realised that I was assuming that you meant that, when the tap was fully open, the water was cold, but when you turned it down to three-quarters, it got hot. If you are saying that the water runs cold until you have opened it to three-quarters, then I would agree that it is probably the sensor or the diaphragm.