Hot water heating

Have a pumped hot water heating system, feed and return type, old, radiators etc.

System was working but pressure too low to get water to top, adjusted, bled,...now can't balance. Pressure keeps building, blowing relief valve when heating. No air leaks, with water feed off condition continues...a blockage somewhere??? Solutions?

Need more info - what type of boiler, is it an open or sealed system?

Pressure building when heating sounds like a sealed system with a faulty expansion vessel. The vessel could be built into the boiler (common with wall hung gas fired boilers) or remote from the boiler - look for a small round tank connected to the pipework, with a 'car tyre' valve on top. (they are often red in colour) It should be charged with air from a car foot pump. With the system drained, you should have about 1 bar of air pressure in the vessel (14 psi)

If there is a lot of noise and banging from the boiler when it's heating, then you could have a system which is low on water, a pump failure, of a blockage which is preventing proper circulation, or a combination of all these.

More details and let's see what we can do.

I'm not an expert, but recently moved into a new house and adjusted some valves near the boiler. Shortly after we played with the valves, we had the pressure relief valve give off water when the system really heated up. A professional came and gave us a bigger expansion tank and adjusted the valves back fully open (weren't to be touched). We have begun to believe that the new tank would not have been necessary once the valves were adjusted back, but we don't know...maybe we broke it by adjusting the valves. It sounds like you may have a similar problem, since you mentioned that you made "adjustments".

We have a similar problem to you where the radiators in the front of the house don't get hot, just warm. The supply leaves the boiler and splits in a T and one side of the T gets plenty of hot water and heat and the other side doesn't. We would appreciate some advice on balancing a hot water heating system with old, cast iron radiators. Can we use the radiator supply valves?

Expansion vessels need to be the right size for the system, and they need checking when the boiler is serviced (BS 7074), and they need to be run at the lowest possible pressure ie. the system static pressure.