Potterton Boiler Locked

[diynoob]

I have Potterton Surema 70. I've had intermittent problems with it for a while but now it locks out when I try to turn on the hot water. I have tried resetting many times but it doesn't work.

Note that if I turn on the CH and reset, the boiler fires up no problem.

I've seen the other threads that recommend a new PCB for lockout problems, but given that it works for CH, is this something different?

 

[Dan Robinson]

Is it overheating when it locks out?

The boielr doesn't actually know what it is heating.

Is your system open vented or sealed? What controls are fitted?

It could be a blockage on the feed pipe as it enters the system - often on the cylinder primaries.

These boilers are VERY easy to overheat.

 

[diynoob]

The boiler is in the kitchen on the ground floor. There is a cylinder in the airing cupboard upstairs diectly above the boiler. In the loft the there is a tank (above the cylinder). I think there's another tank in the loft too. That's open vented yes?

Any tips for investigating or clearing a blockage?

Thanks.