Balancing or sludge?

Some months ago I had a problem with my heating system - newly installed Vaillant 828 combi would heat up to 80 then immediatly cut out without radiators heating up. Same cycle would then continue. A friend checked the boiler and found that the water was circulating through the diverter valve(?) but not through the main pipework. I got a firm in who cut out and replaced pipework near my former HW cylinder (+ filled system with inhibitor) and, hey presto, the rads would then heat up. However the bottom of the rads is always less hot than the top which I presume was because of sludge at the bottom? I've recently replaced two rads but, from day 1, they also do not get as hot at the bottom as at the top. I've tried balancing the system and can get some rads hot at bottom but other rads then get cooler. Should I continue with endless balancing or does the whole system need repiping + new rads in order to cure this problem. (incidently the boiler is sited on ground floor but pipes up to first floor rads before splitting up and down to grnd fl rads and 2nd floor rads - any implications?) It's mostly ground floor rads that have the problem.
Any advice appreciated

I presume you have an old system with a new boiler. Whwn the boiler went in, was the system powerflushed?

The radiators will never be as hot at the bottom as at the top due to stratification (hot water rising).

However if the bottom of the radiators are cold then this indicates a blockage which will most likely require a powerflush to clear.

Hope this helps

Thanks Guys.

Oilman - yes I have an old system with a new boiler and no I didn't have it powerflushed. I've been reading a lot of negative comments about powerflushing on this forum.

The pipework that was replaced was full of solid brown sludge which the engineer said was unlikely to be removed by powerflushing.

....... I didn't have it powerflushed. I've been reading a lot of negative comments about powerflushing on this forum.

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Don't infer too much. If you read carefully, you would see that we are cautious about saying that a powerflush is going to cure any given problem. It has its uses, and when installing a new boiler in an old system powerflushing can be beneficial, especially if the system has not been looked after.

The pipework that was replaced was full of solid brown sludge which the engineer said was unlikely to be removed by powerflushing.

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He is probably right in the case of that piece of pipe, but that indicates that the rest of the pipes are likely to have deposits. This is where powerflushing with an acid descaler is useful. I suspect the problem with the radiators is low flow rates caused by the obstructions in the pipes, and they need removing.

Are you recommending that I get the system powerflushed now?

One concern - is using an acid descaler likely to cause leaks? (....OK not actually cause them, but as my pipework is probably around 20 years old, there may be some joints which are sealed by scale? I just dread finding the boiler pressure slowly dropping and not being able to trace a leak with out pulling the whole house to pieces!)

It might cause leaks, but they could be sealed using a leak sealer. I can't really say that you need a powerflush as I can't see your system. If your heating isn't working properly, and you want it working, then you can take a number of actions. One of these is a powerflush, which is COMPARATIVELY low cost, in the hope of fixing it, before replacing everything.