boiler banging is this the answer?

having changed the pump last year after a small leak blew the pump up, and also a circuit board in the boiler, very troublesome to get the system running again, boiler would fire up for a few seconds then would cut out seemingly over heating. anyway got it all running ok apart from loud banging from the boiler.
Since reading through the forum it seem that it is pobably lack of water either, blockage or whatever. the pump i fitted is a Grundfos which has three speeds, i have always run it on the second speed, would it help to run it on the fastest speed to increse the flow to the boiler thus eliminating the hot spots?
malc

If the system is operating properly then the speed TWO is fine.

To check the flow through the boiler see if the flow and return are fairly similar, ideally about 8-14*C difference between them.

It sounds as if your system is blocked or sludged up. That should be dealt with.

Tony

tried it on fast speed no different i'll try a descaler as we live in a very hard water area. i'm assuming it will take a couple of weeks to work it's "magic"

poping a bottle of descaler has made loads of difference, still pops and goes a bit. think i shall give it another couple of week then maybe another bottle added

Which descaler did you use? I tried the boiler Noise Reducer from Sentinel which worked for a while, then the clonks came back.

Previously I've used the Fernox one which seemed more effective.

Boiler silencers aren`t descalers.afaik........ apparently they coat the surfaces of the boiler and stop the air bubbles forming?.well they stop the kettling anyway

Nige F said:

Boiler silencers aren`t descalers.afaik........ apparently they coat the surfaces of the boiler and stop the air bubbles forming?.well they stop the kettling anyway

Click to expand...

Not very pleased with it, I guess I'll flush it out and use Fernox DS40.

(or is there anything better? Old system but well treated with inhibitor, hard-water area)

i used sentinel descaler together with a bottle of sentinel inhibiter. when the system packed in about a year ago it was out of action for about 5 weeks i'm assuming this didn't help any build up of scale, also after fitting the pump and refilling i neglected to replace the inhibitor

'Scale' formation inside boilers is 99% mythical - if you mean scale formed from calcium (as in 'limescale').

The word 'scale' creates the impression of a layer of hard material stuck to the inside of the boiler. This is indeed what happens inside hot water cylinders, kettles, etc., where water from the mains is constantly added to the contents, bringing in fresh calcium salts.

The water inside a boiler is in a CLOSED CIRCUIT (or should be). If there is anything dissolved in it that reacts with the boiler material or anything else, to form 'scale', it will very quickly be all used up in the reaction and no more 'scale' can form.

The only material able to contribute 'corrosion products' in a CH system is what is there - and its usually the steel in the radiators that's the main source, in the form of iron oxide. In systems which have aeration problems (from air leaks or 'pumping over'), this will be brown sludge - common or garden rust. More commonly, because oxygen is quite scarce, black oxide (magnetite) will form instead. Magnetite has the unfortunate property of forming flakes as well as fine dust, which are both perfect for blocking up small passages inside boilers. In some conditions (mostly, I believe, high temperature-related), black oxide CAN form hard deposits which are very difficult to dissolve - which is why it's a good idea to leave 'system cleaners' in the system for as long as possible within the manufacturer's recommended maximum time. Fortunately, most of the magnetite found in radiators is just lying around in little heaps and therefore relatively easy to flush out.