Hi I have had the Potterton for about 4 years now, and the hot water flow rate has dropped quite substantially. I have tried removing the heat exchanger and descaling it, but to no avail, the flow rate is still low. Is there any other valve that may be sticking that could slow the water rate down? I notice that the burners come on and off while the HW is running, even with the temperature set to maximum, so obviously it is not struggling to heat the water. Any advice would be gladly received.
Potterton Puma 100 poor HW flow rate
- Thread starter Pandobear
- Start date
Thanks for the advice
I have disassembled the inlet isolator and cleaned it all, but there was no blockage there. I have tried to read up on the various formus and people are talking about three way valves being stuck etc, however this boiler does not seem to have a three way valve, it would appear to have two seperate heating loops with the burner heating both, no matter which calls for the burn. On mine this results in the first radiator in the loop becoming extremely hot even with the central heating off if you run the hot water for an extended period. This would not seem to be a very efficent design.
The water flow through gives about half the flow of the cold water tap, is this normal? Perhaps my memory is playing tricks on me, but from what I recall they were very similar when the boiler was first installed.
Again any advice would be gratefully received. Thanks
I have disassembled the inlet isolator and cleaned it all, but there was no blockage there. I have tried to read up on the various formus and people are talking about three way valves being stuck etc, however this boiler does not seem to have a three way valve, it would appear to have two seperate heating loops with the burner heating both, no matter which calls for the burn. On mine this results in the first radiator in the loop becoming extremely hot even with the central heating off if you run the hot water for an extended period. This would not seem to be a very efficent design.
The water flow through gives about half the flow of the cold water tap, is this normal? Perhaps my memory is playing tricks on me, but from what I recall they were very similar when the boiler was first installed.
Again any advice would be gratefully received. Thanks
If your rad gets hot than your diverter valve has failed.
What IS the water flow - measure it with a bucket or something. It's very unlikely to be as fast as the cold, probably about 10 -12litres/min max. But if the burner's going on/off it sounds like it's too slow. Have you checked the wax flow restrictor - you can take it out if you want.
What's the cold flow rate - maybe your pressures just plain low...?
What IS the water flow - measure it with a bucket or something. It's very unlikely to be as fast as the cold, probably about 10 -12litres/min max. But if the burner's going on/off it sounds like it's too slow. Have you checked the wax flow restrictor - you can take it out if you want.
What's the cold flow rate - maybe your pressures just plain low...?
The actual flow rate is 8.5 L per minute on cold and 4.5 L per minute on the hot.
I do not have a manual for this boiler, found one for the 80 which seems similar so will try to find the wax flow restictor that you mention, also the diverter valve.
Again thanks for your onging assistance
I do not have a manual for this boiler, found one for the 80 which seems similar so will try to find the wax flow restictor that you mention, also the diverter valve.
Again thanks for your onging assistance
This is a four pipe and they rarely scale up on this model.
There is obviously some restriction in the how water circuit and the wax stat is the first part to check although I have never seen one failed.
More likely some movable debris is partly blocking an elbow or similar. Its quite tedious searching for this type of fault.
A hose connected to an old flange from a Puma can be used to check the flow at different parts of the DHW circuit.
Tony
There is obviously some restriction in the how water circuit and the wax stat is the first part to check although I have never seen one failed.
More likely some movable debris is partly blocking an elbow or similar. Its quite tedious searching for this type of fault.
A hose connected to an old flange from a Puma can be used to check the flow at different parts of the DHW circuit.
Tony
8.5 l/min on cold is very poor. With such a low flow on cold the hot could well be only 4.5 l/min despite a clean filter/restrictor.
I suggest you check the main stopcock etc and measure static and working water pressures.
I have had to drill out the brass restrictors on these boilers just to get them to fire up on low water pressures (down at 1 Bar).
I suggest you check the main stopcock etc and measure static and working water pressures.
I have had to drill out the brass restrictors on these boilers just to get them to fire up on low water pressures (down at 1 Bar).
I can check the static pressure as this is the maximum that the mains will pressurise the central heating part of this boiler and that is at just over 2 bar.
The house is an old terrace and shares a water feed with next door, most likely lead pipes. There is no blockage in the cold water feed to the boiler and I have just fitted a new bathroom, where water enters house, so it was easy to check water flow rate directly after stop cock. But agreed teh flow rate here is bad. Thames water only seem interested in pressure, not flow rate so not sure what to do there.
I'll replace the wax stat tomorrow.
When I took the heat exhanger out to descale it the central heating side is obviosly larger pipe and was relatively easy to flush through. The hot water side was a lot more difficult with water not easily passing through. the part of the pipes that are visible were not scaled up at all, just some green corrosion that the descaller brought back to clean copper. I have not ever disassembled one before so not sure how free they should be. But to give an example to get the descaling liquid all the way through I had to connect a piece of tubing to one end and blow as hard as I could. Is it likely that this may be my problem? I could strip it down again and maybe blow it out with an air line. What do you think?
thanks again.
The house is an old terrace and shares a water feed with next door, most likely lead pipes. There is no blockage in the cold water feed to the boiler and I have just fitted a new bathroom, where water enters house, so it was easy to check water flow rate directly after stop cock. But agreed teh flow rate here is bad. Thames water only seem interested in pressure, not flow rate so not sure what to do there.
I'll replace the wax stat tomorrow.
When I took the heat exhanger out to descale it the central heating side is obviosly larger pipe and was relatively easy to flush through. The hot water side was a lot more difficult with water not easily passing through. the part of the pipes that are visible were not scaled up at all, just some green corrosion that the descaller brought back to clean copper. I have not ever disassembled one before so not sure how free they should be. But to give an example to get the descaling liquid all the way through I had to connect a piece of tubing to one end and blow as hard as I could. Is it likely that this may be my problem? I could strip it down again and maybe blow it out with an air line. What do you think?
thanks again.
The lower limit is around 9 litres/min flowrate at 1 Bar measured at the boundary stopcock, however the water companies being the immoral unethical lot they are will not even abide by this limit. If you happen to live in a flat a few floors up your boiler may well have a problem since you loose another 1/3 Bar per floor rise.
I have a customer - recent new boiler and unvented setup - complete new system. Pressure in the street is 8 bar. The flowrate was massive at installation until the water company dug up the road to repair the main.
They appear to have blocked the boundary stopcock and the flow is now down to 8 litres at 1 bar. They refuse to do anything about this unacceptable situation. The only course of action is for the customer to pay for a new connection. Mad.
I have a customer - recent new boiler and unvented setup - complete new system. Pressure in the street is 8 bar. The flowrate was massive at installation until the water company dug up the road to repair the main.
They appear to have blocked the boundary stopcock and the flow is now down to 8 litres at 1 bar. They refuse to do anything about this unacceptable situation. The only course of action is for the customer to pay for a new connection. Mad.
I suspect that measured at the stopcock in the street the pressure would be considerably higher, the flow rate certainly would. One of the problems is that these houses are over 100 years old and the feed from the stop cock goes to the old washrooms at the rear of the house, now my bathroom, where it splits to feed two properties. This means that if my neighbour uses water the pressure drops in mine and the flow rate would be effectively halved. I could pay for a new connection but have no idea on the likely cost of this.
To be honest having a combi boiler was really the wrong move for this type of property because even when the system was new and working perfectly you could only really use one tap at a time, hot or cold.
Anyways, any of you guys got any ideas about the heat exchanger?
Thanks again for all the advice, greatly appreciated
To be honest having a combi boiler was really the wrong move for this type of property because even when the system was new and working perfectly you could only really use one tap at a time, hot or cold.
Anyways, any of you guys got any ideas about the heat exchanger?
Thanks again for all the advice, greatly appreciated
I would dis-conect the cold inlet before the filter/restrictor to the boiler and measure the flowrate and dynamic pressure there.
I seem to remember the brass cconnection at the back of the boiler is only 3 0r 4 mm diameter. I had to drill this out to a wider diameter on one particulr Puma as the working pressure was too low to fire it up. The mains was shared between the flat below and the shop cloakroom.
I seem to remember the brass cconnection at the back of the boiler is only 3 0r 4 mm diameter. I had to drill this out to a wider diameter on one particulr Puma as the working pressure was too low to fire it up. The mains was shared between the flat below and the shop cloakroom.
The secondary heat tube is probably in a spiral form and is usually quite small diameter so its not surprising that water does not flow through it easily.
As Geof says its quite possible 4.5 li/min is the max you will get with a poor supply and high flow resistance.
I have a house like that and put in a stored vented system.
Tony
As Geof says its quite possible 4.5 li/min is the max you will get with a poor supply and high flow resistance.
I have a house like that and put in a stored vented system.
Tony
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