hot water goes cold when turned up, please help All aspects of plumbing questions and answers, help, tips and information

[markl34]

I have a combi boiler that gives loads of hot water to the sink taps when on low flow but if you turn them up it goes cold. When using the shower the hot barely gets warm at all. Its a valliant boiler installed in 98. The shower is a new replacement for a manual mixer shower that was there before and apparently had the cartridge fail in it. Can anyone please suggest anything that might be wrong with the boiler or why I cant get high temp, high flow from it? Thanks.

[stevenc1603]

I have a similar issue, but only with the bath. If the hot on the bath is turned to full on the water isn't as hot as it is when turned down a bit lower.

I put it down to the capacity of the boiler not being able to heat that amount of water quickly enough before it passed through the boiler and onto the taps.

[markl34]

I have now had a plumber in to look at the boiler and plumbing for bathroom.
It turns out that there is supposed to be cold water flow restrictor in the shower which wasnt fitted, so that was one problem, allowing too much cold water in and apparently not allowing enough hot water to be drawn from the boiler.
The main problem though is apparently the heater matrix inside the boiler is quiet likely to be resticted due to the hard water corrosion. The boiler also doesnt have (and has never had) an in line water softner fitted. The plumber recomended fitting one before repairing the boiler otherwise the new parts will become corroded too.
I havent had this work done yet but does this sound right to everyone? Would these faults lead to loss of hot water at high flow?
Will post again once work is complete and have results................