Potterton Puma 80 intermittent DHW

[mike.talbot]

Hello,

Im hoping someone may be able to advise....

My 'faithful' 15yr old puma 80 really struggles to provide DHW at peak times, eg getting in the shower at 7am when mains pressure is a little lower than normal due to the rest of the town also getting in the shower at 7am. I've used the old fashioned method of checking the flow rate with a bucket and stopwatch, and this morning it was about 13 litres per min during the morning rush hour. At other times of day, when the mains flow rate is much higher it has no problem providing a constant supply of DHW, however when the flow rate reduces closer to 10 litres per min the DHW cycles on and off.

Is this something simple like a dodgy flow switch?

Answers (and potential solutions) on a postcard please?

Cheers

Mike

 

[kevplumb]

Is this something simple like a dodgy flow switch?

possibly it may be stiff operating or possibly diaphram streched / perished

 

[mike.talbot]

Thanks Kev - just had another go now, and not sure where I was getting those flow rates this morning, possibly still half asleep, but just done it again now and flow rate is about 6-7 litres per min, and the same thing is happening, hot water cycles on/off, heats up fine, cools down again and heats back up about a minute later.

Do you still think its possibly stiff operating or stretched/perished diaphram or maybe something else

Its not likely to be the mains water pressure is it, if 6-7 litres per min is coming through?

Cheers

Mike

 

[mike.talbot]

Thanks Kev - just had another go now, and not sure where I was getting those flow rates this morning, possibly still half asleep, but just done it again now and flow rate is about 6-7 litres per min, and the same thing is happening, hot water cycles on/off, heats up fine, cools down again and heats back up about a minute later.

Do you still think its possibly stiff operating or stretched/perished diaphram or maybe something else

Its not likely to be the mains water pressure is it, if 6-7 litres per min is coming through?

Cheers

Mike

 

[kevplumb]

there is a flow restrictor underneath the boiler you could adjust

6 / 7 lpm ain't gonna set the world on fire

View media item 26358
click on pic to enlarge

 

[mike.talbot]

I'll give the flow restrictor a try

water pressure has never been great, but I havent seen a noticeable drop of late, so who knows!

Cheers

Mike

 

[Beerlover]

Hi Mike, agree with Kev about the DHW flow switch diapragm. Very easy job to change (around £45 for the part 10/18676) This boiler also has a DHW thermostat that restricts the flow until the boiler heats up which will exagerate your flow problems (10/19849) this has a port that can get blocked and is easily cleaned with a small allen key.Under the big nut on the bottom.

http://www.partsarena.com/baxi/

Look on here for the exploded diagram to make things clearer (items 110 & 108 respectively)

 

[mike.talbot]

Cheers Both! I'l first off try adjusting the flow restrictor (easiest & cheapest task lol) then if not perhaps look at cleaning the port (next cheapest task) and then if Im still not winning I'll maybe replace the DHW flow switch diaphragm - no doubt if thats the case I'll be back to ask for more advice!!

Sick of hot and cold showers now lol!

Thanks

Mike