A power flush, or chamical clean (not so effective) is required if the system water is dirty, you have cold spots on radiators due to sludge/magnatite, you have kettling (water in the boiler heat exchanger is overheating causing noise), if you are having a boiler changed (so that no existing system water contamination negatively affects new boiler components and efficiency). I have known customers say that BG have done a power flush before fitting radiator thermostats (This is quite costly on top of having the stats fitted, especially if a power flush is OTT, as often a chemical clean will do the job sufficiently.
Don't get me wrong, a power flush is the best kind of clean, but it's not always necessary as there are other cheaper options available, if circumstances permit.
Thanks for your reply, we had a dripping outside pipe from the tank in the loft. BG came and felt the pipe in the airing cuboard after running the hot water said that the pipe was hot and cold. here it should of been just hot.
Hi Plastic_man77 thanks for your reply My expansion tank overflow in the loft was/is dripping is I replaced the ball float as the old one was under water hoping that it was broken and a simple job at 99p and also took 3/4 of a bucket out 2 days later it was dripping again from the overflow so I called BG as we have a Homecare policy with them. So the BG engineer turned up and asked the problem so I explained he then looked in the airing cupboard went back down and turned the hot water control to on waited a few minutes and went back and felt the pipes at the back on the hot water cylinder and said we have a blockage and needed a power flush. After a cup of tea he got a hose from the van and drew some water from the last radiator and said that it was a bit mucky. When we had 2 extra radiators put in in 2006 the system was drained (not flushed) and a chemical was added during this process. It was Friday when BG attended so I think it will start dripping tomorrow!! The house was built in 1975 a new Potterton boiler fitted in 2000 we moved in in 2005 Regards Ian50
The theory from your BG engineer sounds a little strange. I can't see how a blockage would cause either of your feed and expansion tanks to overflow every few days.
A blockage would stop the transfer of heat to the rads or cylinder and eventually lead to the boiler turning off due to getting up to temperature or overheating. Blockages on the feed side to the cylinder would mean you have no hot water out the taps and a blockage on the central heating side would mean you can't fill the system or bleed rads or the boiler would be switching on and off or overheating as well as your heating or hot water not getting up to temperature efficiently (But you haven't mentioned this in your post).
I suspect that your overflow pipes form both tanks are joined together and you may have repaired the wrong ball valve, or the ball valve you have repaired still passes water in the shut position.
The other explaination could be that water is passing from the heating to the hot water or vice versa, through a pin hole in the coil of your hot water storage cylinder (For this to happen, water levels in your feed and expansion tanks would need to be at different heights).
To test the latter fault, drain the heating and the cylinder water, then undo the unions to the coil and blow through one pipe and put your palm over the other. You shouldn't be able to blow through the coil, but if you can, there is definately a hole. This test isn't conclusive as the hole might only open up when the pressure of water is there and when expansion and contraction is taking place such as when you run your boiler. Do you ever have dirty water out of the hot taps? Put a glass of mains cold water and a glass of hot water side by side and see if there is a difference in clarity.
I have been in the loft today and the big tank is fine but I could see that the small tank was lapping the overflow pipe so with a small bucket and other bits I emptied this tank cleaned it as there was a lot of crud in the bottom released the ball valve and let it fill until it stopped via the ball valve . So the next thing I tried was turn off the boiler and water supply to the hot water cylinder and put a hose pipe on the bottom drain cock but not a lot came out not sure why?? So I did it up again. Also bath / shower water have always been clean
I do not want to drain the central heating system down as it has not been on for some time and it last worked fine the problem has only been about a week. 24hrs later it has started leaking again.
If I understand you correctly, you noticed that the water level in the CH feed and expansion tank was high, so you bailed some water out. You cleaned the tank and then let it fill. Are you sure that there isn't any water in the float, which would cause it to sink over time and that there are no drips at all from the ball valve inlet?
Next, I think you are saying that you turned off the cold feed to your cylinder by closing the gate valve, then tried to drain the hot water from the cylinder by the drain cock at the bottom of the cold feed. The drain cock may not have operated for a few reasons. If air can't get in to the cylinder, no water will drain from it, therefore, you need to open your hot taps. It could also be that the washer in the drain vavle is jammed in position. It is possible to release the washer, but I wont explain that on here, it's high risk and I wouldn't want you to get flooded.
If you don't trust BG 100% and you are concerned that you could shell out for an expensive powerflush that may not have a positive effect on your overflow problem, then you have two options 1) Get in touch with BG and tell them you aren't happy with their diagnosis and want the diagnosis double checked, or 2) Call in an independant heating engineer and see what he says (Don't tell him anything other than your fault symtoms).
Sorry for delay in replying. BG has not been out, tBG were booked to do a power flush, but the engineer whilst draining the system down noticed that the tank was still trickling water and diagnosed that the coil in the hot hot water cylinder was leaking, therefore taking in water from our large tank in the loft and as the level was slightly higher it was pushing through the system and up into the small central heating tank. Result they fitted a new water cylinder and pump. 5 days later it is still dry!! compared to the bucket a day I was taking out of the tank.
Thanks for all your help, in making us question wheather we really needed the Powerflush that was recommended by BG. As the engineer said he would be happy to do it but he said that it would not rectity the problem but make it far worse by discolouring our hot water storage and would then need to come out again and do the work that he carried out above.
You have to take a central heating water sample: 1) Very basic test; judge by color. Black - def. need a power flush Brown - might need a flush Clear like tap water - don't need a flush 2) Advanced; test with TDS and PH meters You will need to test a sample of your tap water to get readings as a baseline. PH - should be close to tap water sample (normally 7.5). Below 6 is a fail, above 8 is a fail TDS - should be within 10% of tap water reading. Tap water is normally around 380ppm 3) We can test your water sample for free, if you post it to us. We will email you the results within 2days.