PLEASE HELP NO H/W NO HEATING

[steve0143]

Potterton profile about 15 yrs old manual valve for switching from heating to hot water. when switching boiler on with valve set to ch/dhw it fires up for about 5 mins then switches off, pipes to pump are hot ,rads cold!! not a lot of hot water then eventually the over-heat thermostat cuts the boiler off.Its a gravity fead system, according to the fault sheet it is a thermostat (is it the gravitydhw/pump over-run thermostat or overheat thermostat or the control thermostat)PLEASE HELP AS ITS GETTING COLD

 

[ollski]

Is the pump running?

 

[meldrew's_mate]

manual valve for switching from heating to hot water.

One of those dinky old Servowarm valves? How quaint
As said, start by checking the pump, you boiler is working

Its a gravity fead (fed) system

Do you mean it's not a sealed system i.e has a F & E tank in the loft?

 

[ChrisR]

Is there an air-bleed point on the pipes by the HW cylinder (near that manual valve)? Air stops circulation.

 

[steve0143]

yes i have the old servowarm manual valve for dhw/ch, have cleaned boiler and checked for air ,it will start up now and run dhw/ch but i have to put immersion heater on for 15 mins before start up then it works fine .Any ideas please???? could it be the boiler thermostat???? Its a fully pumped sytem 2 tanks in loft.