I had a look at the FAQ and couldn't see the answer.
I have a conventional vented central heating system with a Potterton Prima B boiler and a header tank in the loft.
The boiler is very noisy when heating the hot water for the cylinder, even when the boiler is not lit and only pumping - is this kettling?
If so, will I need to flush and treat the system?
I am OK to do this apart from one small problem - I cannot find the drain tap on any rads! The only thing that looks like a drain tap is above the boiler on one of the two pipes at the top labelled 'flow'
The other pipe at the top, I am assuming, is the return - there is a third pipe at the bottom of the boiler which is the same width as the pipes going to the rads - what is that?
If the tap on the flow pipe is the tap I need, how is it possible to get all the sludge out of the rads which are lower than the boiler?
(1) If this is kettling I assume it only happens for a short while after the boiler stops firing? This would be due to the heat left in the boiler after the flame was turned off, like a pan continuing to boil for a little on the hob after you turn the gas off. 'Kettling' does in fact sound like a kettle boiling. If you do have kettling you need to treat your system with Fernox or similar, and flushing beforehand is a good idea. You can just treat, however, by tying up the float valve in the header tank then slowly running off some water by loosening a radiator connection over a bowl until the header tank is empty. Then add your treatment and allow the system to refill. You can also IIRC get treatment that can be injected directly into a radiator through the bleed valve.
(2) There may be a drain on some pipework under the floor (if your pipework does go under the floor). If not, you have a bit of a problem. You need to have a drain tap to allow you to properly drain down.
There are various things you can try - I advise you to get a second opinion though :-)
(a) You can get the pros in to power flush your system - they can take a radiator out to connect in their flushing system.
(b) If you turn off the taps each side of a radiator you can then ease off the connectors, drain the radiator into a bowl, and remove the radiator. You can then flush this radiator out with a hosepipe. If you can work out an adaptor to fit a hosepipe in place of the radiator, you can then open the radiator valve and drain your system. This is then a good time to cut into your piping and fit a drain tap, (you will get a little wet) before re-fitting the radiator. Alternatively you may be able to get a 'T' fitting which connects in place of the normal radiator tap and has a drain tap on it.
(c) You can get taps and connectors which can cut their way into full pipes to form a 'T' junction. These are used for quick fit of outside taps and washing machines or dishwashers. I don't know if there is a suitable one for central heating and I have always wondered where the little bit of copper went :-) However if you can find such a fitting then you could fit a drain tap.
(d) Get one of those 'freezing kits' and freeze your central heating piping at the lowest accessible point. Cut out a piece and insert a drain tap (compression joint would be easiest) before the pipe thaws again :-) Make sure you have enough play in the pipes to allow you to insert the compression joint - if not, you will need a special 'expanding' one which fits into a larger gap then adjusts to fit. You can then drain your system whenever you want.
For A1 full effective flushing it is probably best to take all your radiators off the walls and flush them out with a hosepipe. This is long hard and laborious and prone to spillage of nasty black gunk inside the house. However I have never been convinced that flushing compounds will remove years of gunk from the radiators in a week. Our neighbour had his system power flushed and says the difference was remarkable - however it sounds as though his system was in a bad way before hand - radiators barely heating etc.
This is likely to be because the coil in the HW cylinder is not transferring anything close to the heat that the boiler is producing.
This can be because the coil is inadequately sized (as it can well be in an older cylinder) or because it is furred up. It is also possible that there is a gunging up within the primary side or perhaps a problem with the motorised valve, although I think that's less likely.
Does the boiler cycle on and off a lot when just heating the HW and does the water take a long time to heat from cold?
If it isn't kettling and cycling a lot when running the heating, then something going on at the cylinder is a likely culprit.
I think it's worth flushing the system anyway. You can get one of the power flushing companies in to do the work but expect your wallet to be £500 or more lighter when they have - this is frankly money for old rope.
You can hire the equipment and chemicals and do it quite easily yourself.
I found a better solution is to flush at each radiator position. Basically this involves removing each radiator in turn and flushing water out at each valve. This is better if you have a sealed system, but I've done it fairly well with an open one as well. If you Google in previous threads you will find I posted a step by step instruction on this method.
After doing this, one of the chemical flushing agents run for a week works quite well to mop up most other crud, then a final flushing is done.
However, I have a feeling that the problem may have to do with the cylinder coil. If it's furred up, the only way to tell for sure is by inspection. This involves draining down the hot water system, and the cylinder itself - there should be a drain c*ck near the bottom of the cylinder on the cylinder itself or the cold feed pipe from the roof tank.
You can then remove the immersion heater and look inside with a torch.
If you are in a hard water area and the coil has scaled up, if you install a water softener (a proper ion-exchange one) the scale will gradually dissolve over several months. However, the more realistic fix is to replace the cylinder.
That's to drain at the boiler. The problem is that it is often on a direct path from the header tank in the roof so flushing through it doesn't remove much gunk from the system.
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