Plumbing Question

No water in system (uses oil boiler)

I have placed some new and additional radiators in my system (oil boiler & not combi). My initial problem was not all rads upstairs were re filling with water, so after opening all upper bleed valves it did push some air through but not enough to fully fill the rads. I reckon they were about 1/3 full with the boiler, then switched on, they did get hot until I found a leak. A full drain down and with the leak fixed I turned back on the mains supply. Now it seems I can't get the system to re fill, header tank is filling and ballcock is working fine, bleed valve by hot water tank has water at this point with no air, the boiler will not operate for long as it is overheating, I presume too little or no water in the system. I have tried to shut down the lower floor rads and have bleed valves open but still no sign of any air pushing out or water in pipes. I don't think it's a blockage as the header is clear and fills up, not sure if it's a big air lock ? And if so how best to clear it as the boiler will only run for 2 mins and I can't just run the pump without boiler... arggggggggg
ayn helpful ideas welcome...
Cheers
Rob.

2 Answers

Best Answer

The type of system you have is called an 'Open Vent', this is prone to poor circulation due to sludge/debris build up over many years if neglected. You most certainly still have a lot of air in the system, that's why your boiler is locking out after only a few minutes, the water inside your boiler heat exchanger is literally 'boiling' causing the overheat stat to kick in. There are tricks we know that may resolve the air in the system but as for poor circulation I feel you may need your heating system power flushed before winter sets in.

Contra to the subsequent post by Chris Tomlin, open vent systems IF poorly maintained do indeed develop more sludge & debris then a sealed system. As far as trying to fill your system by his method, it may work, but you are just 'papering over the cracks'. The only way to clean a heating system correctly is to power flush, using a good sludge remover and auxiliary heat source too, as this helps loosen the sludge and any other foreign debris.

Over the past 12 months I have carried out 11 power flushes, 9 were open vent, the remainder were sealed systems and the open vent systems were by far the worst in terms of sludge build up. Remember we can only advise, your call at the end of the day.

On a foot note I do agree with Chris Tomlin that open vent systems
have been around for may years and are a reliable system, but home owners tend to pay little attention to the cleanliness of the heating circuit and just focus on the boiler maintenance regime instead.

Answered 28th Sep 2013

Boiler Homecare

Member since 6 Jan 2010

Hello, open vented systems are fine if installed correctly, I have worked on this type of system that are 50 years old and still no problem. Put a hose on the cold tap and connect it to the drain point on the heating, open the drain valve then open the tap slowly get a mate to start venting the rads. You may get a small flow up to the tank so be careful. Most plumbers will use this method when they have trouble filling a system. If the system worked before stay away from power flushing most the time it is completely unnecessary.

Answered 29th Sep 2013

chris tomlin

Member since 28 Mar 2012

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