Boiler problem

[vauny]

My oil fired boiler will heat the water with no problems but when I put the central heating on, it's failing to maintain a suitable water temperature
The central heating side of it works but seems to affect the hot water side.
When both are called for the boiler will run for ages and never seems to acheive a high enough temp to cut out

[scorpious321]

oil fire boiler might be under rated, has anyone added any extra radiators to your house eg exstention eg radiators could be robbing the hot water flow pipejust a thought try and balance down your radiator vavles nearest one first and so on and look at the by pass aswell balance that down if you have one ?

[vauny]

Thanks - no the installation is original - this problem has just occured - its been fine up till now.

[scorpious321]

hi vauny you say the problem has just occured, has anyone touched the three way valve. have you had a new put in recently might be put in wrong way round,or old one playing up,just a thought ?