DIY Doctor

power flushing

Postby mtoogood » Sun Jun 29, 2008 10:45 am

i had british gas in to service the gas central heating system in my house. they recommended that we have the system power flushed (never touched in 20 years apart from 2 building projects and boiler replaceed in the interim)
2 radiators dont work and the system got blocked and pump failed last time i drained down. when it was got work (by br gas) they pointed out that the system was 'pumping over' into the header tank and that this would cause long term damage if not power flushed
i got a plumber who specilaises in power flushing to come and flush the system last week. he spent about 5 hours doing it connecting his equipment where the pump is normally.
anyway he left, the same 2 radiators still dont work and the system is still pumping over into the header tank.
i get the impression that he hasnt done the job properly/completey
any comments (naturally i paid him in full when he had done the job)
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Simply Build It

Postby Skids » Sun Jun 29, 2008 9:49 pm

Hi mtoogood,

If BG serviced you CH system WHY did they not sort out the problems, is it on contract,

There is a difference between ‘service’ and ‘fault find’ !!

I would check the contract and if required call them back!!

Silly question? Did you ask him to fix the problems (2 reds and over pumping) or just power flush the system?

The 2 rads might have been sludged up, however they may also be something else!

Same for the over pumping

If you did,

Did he show you what he had done, did he test the system and did you touch the WORKING hot rads to see that they where working, and look in the F&E Tank to check that it was not over pumping?

There should be a guarantee period!

Call him back!!

Best of luck

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Postby EyeTry » Sun Jun 29, 2008 10:05 pm

Radiators have two valves - one to control the actual flow through the radiator (and will be set slightly different to the next radiator on that pipe circuit - and that with the next etc) - and the other valve will usually be a thermostatic one so you can set the room temperature. A proper temperature gauge is clipped to the inlet pipe and another to the outlet pipe and the flow valve adjusted until there is a several degree difference to the IN and OUT reading. The difference is what heats the radiator and therefore the room.

I wonder if the engineer went around opening both valves to their maximum and therefore permitting the best possible power flush.... and then of course went around afterwards balancing the flows and re-setting the theremostatic valves or whatever valve you have in your system.

And as soon as you add fresh water to a system - even one with a commercial system care product e.g. Fernox - and heat it you release trapped oygen into the system - which collects in high points - like tops of radiators - and requires bleeding. Bacteria in an unprotected system actually produces nitrogen and the general reaction of steel radiators and copper pipes adds to that issue. Bleed some water off (radiator key, plastic jug and a few rags to catch any spray / drips) and see how clean or black the water is. I`ve used Fernox system cleanser (and several flush throughs before the days of Neutraliser) and the system care product AND THEY ARE GREAT. Not Needed to bleed my system for years. (Fingers crossed)

An easy test re the pumping over is the fact that boiler pumps have two or three speed settings - may just be a slot-type bolt head with I, II, or III markings. Try turning it down one and see if that resolves the pumping over.

The overflow pipe back up to the CH header tank (NOT the cold water tank as per my neighbour`s - that overflowed and brought the bedroom then living room ceilings down during their holidays - messy). That connection should be on the hot flow from the boiler but before the pump - otherwise the pumps pushes the flow anywhere it will go and the overflow would be the nearest and easiest option.

Another possibility could be the boiler temperature is set too high and hot water expands - and would go up an overflow as per design. You would expect to hear big "gurgles" as the too hot water went up the pipe but I don`t think you`d get the same sound if it was being pumped up the overflow.

Me - I`d try bleeding and that pump setting. Straight forward jobs and if no good you can check what the plumber said was the problem(s) reported by you and then what he said he did to rectify same. Good luck EyeTry
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Postby htg engineer » Mon Jun 30, 2008 8:31 am

Could this be another case of a certain company just wanting money off a powerflush - whether the system works or not, they wont be bothered.

I know people that have worked for them, and they complained about how they had to offer powerflushes - even if they weren't needed. Boilers over a certain age, repair ?? no... try to sell a new boiler. Why ??? money.

I've never met one person with a homecare package that is completely happy with the service.

Anyone that has a service package with these will be ripped off at some point.
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Postby Sidspanner » Sun Jul 27, 2008 6:39 pm

On the subject of power flushes, how long should it take to power flush a system with 10 radiators? i realise that some workmen will do the job quicker than others, but what would be an average sort of time for that job?
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Postby htg engineer » Mon Jul 28, 2008 8:29 pm

On average about 4 - 5 hours, depending on what is coming out of the system it's obviously no good stopping if there's still debri's coming out and the water is not clear - so anything up to 7 hours. They should also call 2 - 3 days before the visit to dose the heating system with chemicals to loosen the stubborn scale and sludge.

Also make sure they add inhibitors - otherwise you will get the same problems again.

Plus most companies charge a few hundred pounds for powerflushing, £350+. So if they're there for only 2 hours - don't pay them, or at least ask for a reduction in the price. 5 hours at £70 (£350) + chemicals isn't bad. But £175 per hour ?? no way.

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Postby Sidspanner » Wed Jul 30, 2008 6:51 pm

thanks htg engineer, that was exactly what I wanted to know. I mean Joe Public has no idea whether tradesmen ( cough) are actually doing what they are supposed to be doing. At least now I have a rough guide. Incidentally the power flush thing was prompted by a visit from British Gas engineer who held a magnet on a copper pipe and said " that shouldn't stick to that pipe, it's only doing it because the pipes are all sludged up". It sounded feasible, and started us thinking about a power flush before the winter came in.
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