Powermax 155

[philipbuckley]

I have a powermax boiler which is about 6 years old. It started to make whistling noises at startup some weeks ago, the noise would last for about 20 minutes and then die off, other than that the system still seemed to work okay. 2 weeks ago downstairs rads went cold (this was not a gradual processs). I changed the pump that feeds the rads (the system has two!). this did not make any difference. If I switch rads off upstairs a limited amount of warm (not hot) water is fed to the downstairs rads. I called a plumber in, he was no help and charged me =A358 for telling me he couldnt fix it. I called in Potterton who said that they could find nothing wrong with the boiler (we have plenty of hot running water). They have put a descaller into the system, X400 and told me that it could take up to two months to have any effect (that is asuming I have a blockage) the engineer also took a sample of the water and that's the current situation. On this limited info has anyone got any ideas on what could be wrong and how I can fix it. I know nothing about central heating systems but I am mechanicaly minded and was able to replace the pump which is happily spinning away but not pushing hot water around the system (when I take the bleed cover off a bit of water trickles out), the pipe going to the pump is cold as is the one leading from it. Help!

[Aidan]

They are a combined boiler & thermal store.

If the radiators upstairs are hot & those downstairs aren't, it suggests gravity circulation, i.e. the CH pump may not be running. There might be water flowing through the pump, due to gravity circulation, causing the pump rotor to spin & so giving the impression the pump is running when you remove the central air vent plug. If there's hot water, this is the other pump, so this tallies. You get gravity circulation with these because they contain 100 litres of hot water.

If you're electrically competent & have a multimeter, check there's power to the CH pump (terminal 25) when the heating is called for. Check the obvious (programmer, room thermostat, etc.).If no power to pump, check the cold start thermostat. This disables the CH pump until the thermal store is at 60 degC (I think) or above, to prevent flue gas condensation.

There's also an auto air vent on the top panel, at the back, under a cover (not on open vent models). Unscrew the top cao (similar to a car tyre valve cover) to vent any air. There's also a low water level switch, but I think that disables the burner and pumps.

[Aidan]

Having looked at the manual, there's a fault finding chart on P12.

It says, if no CH, Is the appliance/programmer/roomstat calling for heat, i.e. 240 V at terminal 28?

If yes, check the cold start thermostat (domestic priority stat) it will not allow CH if the cylinder store is below 65 degC.

If OK, check pump & connections at terminal 25 & N2.

[philipbuckley]

[philipbuckley]

Hi Aidan, Thanks for your time. The pump seems to be working, in fact it is. When I switch the room thermostat on and off the pump responds immediatly so the roomstat is calling for heat. Unfortunalty I have no manual to refer to and have not looked beyond the front of the boiler and have not got a clue where the 'Cold start thermostat' would be. Also I am not sure if this is open vent model or not but will take the top cover off to see if I can see a vent valve.

[philipbuckley]

Ive now checked the vent and it is open vent model so that's that out of the way which leaves this cold start thermostat, where is it?

[philipbuckley]

I have now also checked terminal 25 and this gives a reading which corresponds with the pump that is definitely turning under power rather than gravity force

[Aidan]

If the pump is running, then I'd think it isn't a boiler fault but a blockage in the downstairs heating circuit. Any valves, rad valves TRVs that might be shut? Have you bled the radiators? It could be black magnetite sludge, from corrosion of the inside of the radiators. You can get a magnet to stick to the outside of a copper pipe if the pipe is blocked with magnetite sludge. Try testing any low points or elbows near the boiler. Any corrosion inhibitors in the water?

If it is sludge you'd need to flush/powerflush the system to try to remove enough to clear a flow path. Search this group for more information. It is horribly adhesive; although thorough powerflushing is the best method of shifting it, I doubt that you can ever get all of it out.

[philipbuckley]

Thanks Aidan I think you are serving to confirm what i am now thinking and that is that I have a blockage. When I take some water from the rads it is brown from some and black and sticky from others. The system did have inhibitor in it but i have not kept a check on the concentration in the years we have been here and it certainly has not been checked in th last two years. My concern with power flushing the system is that I have all plastic piping (some microbore) and it is all connected together with these push fittings, I have no confidence in these and I am concerned that they would blow apart under pressure. Would I acheive anything by just draining the system down and refilling it?

[Gav]

in actual fact push fit such as hep 2o and speedfit perform better under pressure, obviously depending in pressure, not toooo high!

can you ( depending on boiller config) just open both ends, ie inlet(mains supply) and outlet ( system drain point) it should be able to withstand mains pressure at least. when fittings are tested and properly made they use immense presures mainly for insurance purposes!

they dont want claims for knackered ceilings!

even taking each rad off one by one and slapping jet wash on it would reduce the total amount of crap in system.

hope this helps, if not i hope it's funny

[janie]

Interesting post.

I'm thinking of replacing my Powermax 155, as I want to put the boile in the loft & it's far too big & heavy!

Does anyone have any idea of what the output is from one of thes beasts please. I've tried all over the internet & can't find out.

I've had a quote for a Worcester 28 I, but don't know how it compare on KW/BTU with the existing boiler.

Thanks for any help you can give me

-- janie

[Heliotrope Smith]

Try the Potterton site. Think these are in two sections.