Bleeding Radiators

[Roger]

Hi We move into our current home last April and had a new boiler fitted in July, the rest of the system was not changed, its all working fine but I just have one concern.

I find that the heated towel rail in the bathroom needs bleeding every couple of days, does this mean that I've have a leak somewhere?

The system is the type with a pump and header tank, I forget what you call it.

And advice gratefully received Many thanks Roger [e-mail]

[Christian McArdle]

Usually. However, there are other causes of gas in the system in a open vented system.

1. Corroding iron/steel components such as radiators can cause hydrogen to form. You can test for this by collecting the bleed gas in a test tube and attempting to burn it with a splint. A pop indicated hydrogen. This is solved by draining down the system, flushing it and refilling it with corrosion inhibited water.
2. Pumping over. If the system is poorly designed or implemented, the system water can be returned to the tank through the vent and back down the feed line. This enables air to enter the system, which can aid corrosion and be found whilst venting.
3. Overflow in operation. If for any reason water is continuously dumped out through the overflow (i.e. bad fill valve, inappropriate tank water level or bad pumping over), then new water enters the system. Water from the mains has LOADS of entrained air that will enter the system. The overflow often only operates when the system is hot, or during startup or stopping of the pump, but this is enough to cause problems.

Although (2) and (3) above can be fixed, it is often easier just to replace the old feed tank with a proper system pressurised from the mains. This means putting an expansion vessel and pressure relief valve on the system. In the US, it is typically filled via a PRV, whilst in the UK, a manual fill valve and pressure gauge are used to prevent contamination of the mains supply and to ensure that any loss of water is noticed, rather than continuously replenished without any sign that immediate maintenance is required.

Christian.