hot water stops when cold water tap is turned on Information, help and advice on many gas related subjects from gas fires to domestic appliances

[uk_ducati]

hi all,
i am currently working towards my ACS and was wondering about a problem my mother has had with her water heater for many years. When she runs the hot tap the heater lights up and heats the water fine, but if she then turns on the cold tap or flushes the toilet the water from the hot tap stops being heated and eventually runs cold (at the same time the flame reduces in size in the water heater). i was wondering if this could be something to do with the cold water flow rate being reduced into the water heater or could it be incorrect pipe sizing. i have had a look at the pipe sizing and i think it is too small for the amount of appliances it feeds. i have not done all the calculations yet but initial thoughts are they are too small.
any suggestions would be a great help
thanks

paul

[htg engineer]

It is to do with the flow rate to the water heater maybe not that it's poor or it has altered over the years - more likely the diaphragm in the water heater.

Over time the diaphragm will become stretched and possible split, this will alter the flame size and the temperature of the water when more taps are used, it's nopt that the flow is inadequate - there's just not enough to take up the slack of the diaphragm.

Replacing the diaphragm should slove the problem, changing procedures vary and some can be quite awkward. Quite a common part to need changing so there'll be a detailed diagram and instructions on how to change the diaphragm in the appliance instructions.

Htg

[uk_ducati]

thanks for that but would this be the problem as it has happened since brand new.