Hot water only from my bath tap

[Tudor]

I have a Saunier Duval sd623 combi boiler, approx. 12 years old. For the last 6 months I have only been able to get hot water from the bath taps. The hot taps for the sinks in the bathroom and the kitchen do not produce hot water. For some reason they do not fire up the boiler, it remains with the pilot light on.
When I turn the bath hot tap on and then the kitchen sink hot tap on I only get a trickle of water from the kitchen tap (I use to get more than a trickle with two hot taps on). If I then turn the bath tap off the water comes through fine and hot from the kitchen sink tap and the boiler remains fired up. As soon as I turn off the kitchen tap the boiler goes back to its pilot light state and won't fire up again without the bath tap been opened first.
The central heating appears to be working OK, in that the boiler fires up when required to do so and all the radiators are hot.
The water board did replace the water mains to my block of flats about the time it all started going wrong but I don't know if this is a coincidence.

 

[breezer]

i am not a plumber or heating engineer, but it sounds like a partial blockage to the boile feed, because you said The water board did replace the water mains to my block of flats about the time it all started going wrong

 

[MANDATE]

To add to 'breezers' response there are a few aspects to consider.
The mains pressure is at its highest at ground level so the higher you are in your block of flats the lower the mains pressure.
I think the partial blockage could be scale, this would have built up over the 12 years and is more likely to be in the heat exchanger and the pipe from boiler to taps.
As the scale builds up the inside diameter of the pipe reduces which would explain why you only have trickle from the kitchen because it will be already be a smaller pipe than the bath pipe. Water is reluctant to go through a small pipe when a larger one is available.
The scale also acts as a insulator so the water cannot reach the designed temperture.
The flow of water depends on the 'force' pushing it and the 'resistance' preventing it, so it would appear you have too little of one and too much of the other.
Just my opinion! I'm not a plumber either

 

[Tudor]

Thanks Breezer & Mandate for your responses.

I have a first floor flat and do live in an area which has hard water and the associated limescale. If this is a blockage problem then I would envisage that having the whole system flushed would be a good idea, would you agree? I am not that good with the DIY stuff so would most probably get a chap in to do it for me, or is this something simple that I can do without anything going wrong. Do you know how much you think it should cost for a combi boiler and seven radiators?

 

[oilman]

Cost for power flushing, about £300 to £700.

.......or is this something simple that I can do without anything going wrong.

Well, things go wrong for me, they just have to be sorted out quickly.