Posted: Fri Mar 19, 2010 2:55pm

toni i have a pressurised system on my boat it nis a morso backboiler oil fired feeding three rads with a johnson circulating pump i would like to know at what pressure it should be set at the pressure is set via a filling link i think the system is the same as house system hope you can help many thanks

Posted: Fri Mar 19, 2010 5:52pm

I regret that if you are correct about it being a sealed system then I have no alternative other than to point out that a thermostat failure on the stove could result in an explosion unless a pressure relief valve of sufficient size has been fitted. In that case the valve outlet could vent considerable quantities of superheated steam. being oil fired it will be safer than a solid fuel stove but I will not answer your question. Basically you need the AIR pressure in the vessel to be sufficient to minimise the amount of water in the vessel when it is cold. In this way the expanding hot water will have somewhere to go. The filling link should only be used to top the system up when water has been lost. The more water you put in the less expansion room there will be. Perhaps a reader with knowledge of domestic central heating might give some more information but failing that I must advise that you contact whoever fitted the system. Tony Brooks