Possible 3 way valve problem?

[robblowen]

I've got a potterton performa 24 boiler which has stopped working? Its got power, pump starts when either central heating or hot water is turned on but the boiler doesn't ignite. When the hot water tap is turn on the pressure differential part of the valve works which presses the micro switch on the front. When the central heating is turned on the hot water priority part tries to operate but doesn't seem to have enough movement to press the micro switch. If I operate the micro switch manually the boiler ignites and heats the water. Hope this makes sense and someone can point me in the right direction.

Cheers in advance.

 

[Joe4542]

When you say "hot water priority" bit, I presume you actually mean the flow differential switch that pops up vertically?

This not coming up properly suggests you have a flow/circulation issue.

Given you seem to be suffering on both CH & DHW it normally means inside the boiler.
Something as simple as partial blockage in the bypass/pressure sensing ports can cause it, a slow/partially blocked pump or worst case restriction inside main heat exchanger.

 

[robblowen]

Cheers joe, yeah I couldn't think of the proper name when writing the post but I've checked the MI and it is the flow differential switch. Is there a simple way to flush the system or will it be best to get a plumber out to sort it?

Cheers.

 

[Joe4542]

Simple way? Unfortunately no, without having a flushing machine (even then, they're not great at flushing thru boilers), it can mean taking the boiler apart to flush out the main h/ex with a hose or like.
That means working within the airbox casing, and rebuilding, which unfortunately is not something a DIYer should be contemplating.

You could possibly try disconnecting flow and return pipework and mains flushing thru them to a drain, but again, whilst simple in theory, not a quick and easy job in reality.

Again, it could just be a blocked port in the flow differential, or even just a split diaphragm in there. But you could waste a lot of time, it would usually be quicker/easier (admittedly with cost) to just let someone who knows what they're doing.