Hello Everyone,
Newly registered today, but have read many posts before on this great site. My problem, is with a Potterton Profile 60 boiler.Central heating/hot water works fine but when hot water only is selected, the bolier fires up and cycles on and off for a while then trips the overheat thermostat requiring manual resetting.
The system is Open vent,gravity hot water and pumped central heating.
The pump seems to be running o.k (set on 2) Also Im very confused..cant seem to find a diverter valve anywhere..what stops the heated water from entering the heating circuit when water only is selected ??
Any help greatly appreciated.
Thanks.

Sounds like the water isn't flowing round the DHW gravity system - My first thought would be to drain and refill the system, see what muck you dislodge, is there a drain valve at the boiler on the DHW pipes ?

I expect somemore comments soon so see what other ideas there are before you dive in.

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We have a conflict for starters, you say it's an open vented gravity hot water system, then you say the pump seems to be running ok.

Have you been playing with anything, turning the bathroom radiator/towel rail off for example.

Provided you have gravity primaries then you may not have a divertor valve, which would have been optional, again there are settings on the boiler for fully pumped, gravity or sealed systems, this would have been setup when the boiler was installed, and must not be altered.

Is there an air vent on the cylinder where the primary pipes connect, and has the header tank got water init.