Yet another Powermax 155x problem

[chris558855]

Powermax 155x, approx 6 years old, had new programmer a year ago. The fault is that in general I can only get hot water when the central heating is on. Although sometimes can briefly get it if just water turned on and boiler cold, but once it gets to temp doesn't ignite again and hot tap soon running cold. It does not appear to be heating the water in the storage tank, the second the burner stops so does the hot water. Hot water pressure/flow is still ok. Does this point to the blending valve / pump or other?? Many thanks

 

[Kristoflampie]

Check the circulating pump for the store........ sounds like its failed so burner only heats the store a bit until it cuts out on temp

 

[chris558855]

Am I right in thinking that is the pump under the heat Exchanger?

 

[Kristoflampie]

bottom right of unit??..... pipes are usually marked

 

[chris558855]

Thanks will check it out, not home until Tuesday though.

 

[chris558855]

Book lists a Myson CP51 for the heat exchanger pump anyone know a cheap source if it is the pump? Parts Center around £92 for a CP51, but can get a CP53 delivered off ebay for £38 would that fit??

 

[Agile]

The CP51 is a single speed pump equivalent to a CP53 on the highest "3" setting.

I would therefore expect a CP53 to be a pump head replacement for the CP51 used in your boiler.

Tony

 

[chris558855]

Unfortunatly it's not the pump at fault, both pumps seem to be fine. switched on from cold it makes hot water until it reaches temp and then won't start again unless heating switched on. Once the boiler has lite for the heating you can switch the heating off and it continues to make hot water until it reaches temp again. Is it likely to be a faulty Flow Switch/Relay assembly? (The flow switch is leaking anyway!!). The other thing that concerns me though is that once the boiler switches off the hot water goes cold in seconds, so it does not appear to be heating the storage tank. Many thanks again.....

 

[Range185]

First port of call for this issue on the Powermaxes is the blender valve (Part P757) as this is the main culprit for limiting hot water supply, as they get scaled up easily.

 

[chris558855]

From other queries I have seen on here, if it is the the blender valve do you not usually loose pressure / flow on the hot water taps? Pressure / flow is still very good.

 

[Range185]

I didn't have a problem with water pressure on mine, it just simply cannot produce enough hot water, so provides luke warm then cold water. It's most likely to be the blender valve that needs changing.

If you don't have any ignition problems then it won't be the electrode or the PCB, which leads me to believe its the blender valve, as its a major culprit on the Powermax for failing.

Does it cut out, ie not re-ignite, because that could indicate a lack of water in the thermal store (safety cut out). Have you drained it down recently ?

 

[kevindgas]

From other queries I have seen on here, if it is the the blender valve do you not usually loose pressure / flow on the hot water taps? Pressure / flow is still very good.

very rarely do you lose pressure it just mixes wrong, too much cold is the usual problem, often caused by a combination of cr*p water and scaling on the hot water coil.

 

[chris558855]

as long as the green burner light is on, the hot water is very hot for as long as you run the tap. If you turn the tap off and the boiler gets to temp and the green light goes out, the water goes cold very quickly and the boiler does not atempt to relight unless you turn the central heating on, then water very hot again probably for as long as you want it. Which is why I was going for the flow switch/relay rather than the blending valve??

 

[chris558855]

Hi, replaced the flow switch and relay (it was leaking anyway and the relay casing was cracked), but should have listened to you, still no joy. Will go for the blender valve next!! Do you know what gaskets you get in the PMAX P493 SERVICE GASKET SET, does it include the burner gasket? Many thanks Chris

 

[Gasburner]

The Powermax 155x is a thermal store unit, the cold start thermostat should prevent the heating pump from operating until the thermal store is at least 60C. The thermal store is set at 80C max. If the heating is turned on the pump will dump the contents of the thermal store to the rads, this can result in there being insufficient heat left in the thermal store should a hot tap be turned on soon after. When a hot tap is turned on the flow switch starts the 2nd pump (Right Hand ) which circulates the thermal stored hot water through the plate heat exchanger which in turn heats the DHW which then passes to the blending valve to maintain a flow temperature around 60C at a max flow rate of 12 ltrs per min. Is the pipe between the plate heat exchanger and blending valve getting hot when the tap is turned on? If it is but the temperature of the out let from the valve is not then try adjusting the blending valve. Hope this helps.