Combi - can't use hot and cold at same time

[mallangong1]

Hi,

I posted s imilar question a while ago but have got more information - which I hope will lead to an answer.

I have a Potterton Puma 80 combi. Water pressure is good - 3.5 bar. Cold water flow is 16 l/m. Hot alone is around 8 l/m. However when both the hot and cold are run together the hot flow reduces to below 4 l/m.

At this flow the boiler keeps cutting out (presumably as the flow is too low), so not only does the hot water end up being low but it goes in waves of temperature.

I had a couple of plumbers around. One said I needed to move the boiler to the centre of the house but that I may just have to live with it. The other said that a new boiler should sort it. He recomended a Potterton Gold 33 HE A which including fitting would be £1,150.

Which is right? And if a new boiler is that model and price good?

Thanks,
Jim

 

[Agile]

You should have continued your previous thread.

It sounds as if you may have a restriction in some of your internal pipework.

The flow switch on the Puma should operate at about 2-3 li/min and can be adjusted if its in good condition.

At low DHW flow rates the Puma is very sensitive to minimum flow rates and will get the water too hot and turn off the burners.

The effect of this is to make the correct gas settings on the boiler very critical. That needs checking/setting by a registered gas engineer.

Running a hot tap at 1/2 flow rate may help if its at a shower that you are asking.

You dont say what cold water use you are making. If its on a shower then you should use more hot flow and reduce the temperature setting knob on the boiler.

Tony

 

[mallangong1]

Thanks agile, - happy for a moderator to combine them if possible.

I don't think it is a restriction as it even affects the kitchen tap and I have visualy inspected all the pipework from there to the boiler 3 feet away.

This affect happens on all taps in the house, as soon as the cold is being used the hot flow reduces drasticly (whether that be using the mixer shower or even just the toilet refilling at the same time as runing the hot tap).

Do you think a new boiler like one plumber suggested would solve this? If so did his suggested make/model and prices sound ok?

 

[Agile]

That would imply a very limited cold water flow rate into the property ( or stopcock not fully on ).

But you say you have 16 li/min ( presumably open pipe ).

The flow measurements you quote dont seem to be compatible. Or you have a restricted pipework in the house?

Are you confident your measurements are correct? Tap measurements should be made with all outlets open at the same time so they dont interact.

Tony