Central heating coming on by itself

[Chris]

I have a Ariston a\23 boiler for hot water and central heating, and over the past week it has been coming on by itself. The thermostat is turned down, timer is off on the boiler and it is on summer setting i.e.. hot water only. The only way to stop it is with the power switch, when switched back on it goes back to hot water only, for another day or so.

TIA Chris D

[Ian Stirling]

Broken 3-way valve? Boiler signalling 3-way valve to go the wrong way?

[Dave Plowman (News)]

Sounds like the three port valve sticking.

[Chris]

Thanks,

How would I pin point what is causing the fault, I can see from the servicing instructions that the 3-way valve is made up from: a bypass kit, pressure switch, 3 way spring, diaphram valve, microswitch and a main flow switch.

Is it a case of taking this to bits and seeing which is faulty, or how do I test what is controlling the 3-way valve.

Thanks Chris D

[Ian Stirling]

Do you own a multimeter? Connect something to indicate when it's signalled to be in one position. (Lightbulb, multimeter, ...)

Find out if it ever gets in the wrong position for the input signals.

[raden]

I doubt it, if it's just started happening.

[Ian Stirling]

True. Boiler electronics can fail in unusual ways though.

[ski]

[raden]

But not really like that

I can't picture the Ariston a23 by that name, but the pcb gets the SWL/thermostat/clock signal which starts the heating sequence. If the diverter valve needs to move, the pcb will power it up and, if necessary, wait for the signal back to say it's in position.

[look]

How about a fault frost stat ?

Easy to check anyway - disconnect

Robert royall at which net

[Chris]