DIY Doctor UK DIY Forums

When the boiler is set to hot water it runs until the pipes are banging then (overheats ?) and shuts down. After approx. 10 mins the system resets and is ok again.
The central heating works perfectly
I replaced the HTS3 thermostat on the cylinder but then noticed that the mid position valve was stuck on H regardless of the system setting. I turned off the power, removed its cover and sprayed with WD40. Works fine now.
The on/off switch on the HTS3 works fine too.
The house/system is 8 years old if that has any relevance.
Any advice would be most welcome
Puzzled also as to why the water got hot even though mid position valve (679H340-3olo) was stuck on H - not aware that any radiators where hot.

sounds to me like the motorised valve is faulty. take off the motor and give the spindle a few turns

Standard Y plan electric set up does not go through valve for hot water, it does however go through the valve for central heating so if valve sticks in central heating (Fully open) the boiler will run when hot water calls but hot water will not get hot. Do an internet search for Honeywell Y plan and you will see what I mean.