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Flush sealed system

Postby sadsyndrome » Sat Oct 27, 2007 5:42 pm

I have a sealed system with an expansion vessel under boiler in a Halstead System Pod (vessel, pump pressure relief valve etc).
Boiler is making banging noises so I though that I would flush out, use cleaner, flush again and then use inhibitor. I have managed to put the cleaner in and heating is now back on, but I have a couple of questions before I do the next flush.

Q1. Today, I used a drain valve on low point of pipework and just let the system empty into a drain via hosepipe. I opened bleed valves in all rads and flushed system for 10 mins with fill loop, then closed drain valve & used towel rad to insert cleaner & finally filled system. Is this all I need to do or do I have to remove CH pump to flush system properly? How long do I have to flush system via fill loop, before closing drain valve?

I think my towel rad (highest rad) is acting as the expansion vessel. There is a cold part at top which seems to get smaller when system heats up. The expansion vessel (1.5 bar) has a metal braid pipe which is always cold and the guage showed 2.0 bar when the system was hot. I thought hat the braid should be hot especially when system was up to 2.0 bar? Is there any way this braid could be blocked to prevent the vessel from doing its job? Does anyone know how I can check the exp vessel is operating correctly?

thanks in advance
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Simply Build It

Postby htg engineer » Sat Oct 27, 2007 9:07 pm

There's no need to remove pump, where is the drain point, and which way are the downstairs radiators fed ? If the drain point is near the boiler and the downstairs radiator pipes come down from upstairs, then your not draining the whole system, all downstairs radiators should be removed and emptied. If the radiators are fed from under the floor then draining from the boiler is ok.

As for the towel rail if the top is colder than the rest of the boiler then it will just need bleeding as it has air in it.

When the heating is on the pressure gauge should rise abit, 0.5 bar is a perfectly normal increase due to the temperature of the system and the effect the pump has on the pressure gauge. If your expansion vessel wasn't working the pressure gauge would rise to 4 bar then it would discharge via the pressure relief valve on the boiler. Then the heating wouldn't work until the system was re-pressurised.

I hope this has answered your questions.
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Postby sadsyndrome » Mon Oct 29, 2007 8:19 pm

My d/stairs rad are fed from underfloor. The drain point is also coming off this underfloor pipework. I just wondered whether draining/ flushing would fill the pump up with debris. I'm glad that you say not cos the pump is a bit difficult to get at!

I will bleed out the towel rad as you suggest, but as my guage was at 2.0 bar so I thought that the exp vessel pipe (metal braid) should be hot and the guage should have stayed at about 1.5 bar (assuming exp vessel was set at 1.5)? I was concerned that if exp vessel is not working and I bleed air from towel rad the expansion won't have anywhere to go so pressure may go too high.
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