Combi Boiler-Hot rads but intermittent hot/lukewarm water

I have a Ravenhead Combi boiler which is just coming up to 5 years old. It chucks out plenty of heat for the radiators but am having trouble with the hot water. First of all it comes out hot, then it goes cold, then its lukewarm, then I have to turn the flow down considerably to get hot water, so on and so forth. An engineer looked at it sometime ago and said it was a sludge build up - do you think this is a classic symptom of sludge. He only looked at the boiler and didn't actually see "inside" anywhere to see the sludge. The boiler is not noisy at all, and apart from the hot water problem it works fine.
If it is sludge, can I try to desludge it myself?

Being a female, I can cook, clean, look after kids, diagnose computer problems, excellent at painting and decorating, can fix most things and will attempt any task, but I'm afraid have had no experience of plumbing issues !!

Being a male, I can cook, clean, look after kids, diagnose some computer problems, excellent at painting and decorating, can fix most things and will attempt any task, and have some experience of plumbing issues but particularly I specialise in fixing boilers and heating systems!!

As you have not specified which of the many Ravenheat boiler models you have then I cannot speculate in detail what your problem may be. However sludge does detract from hot water performance when the system was not properly cleaned on installation.

Tony Glazier

Excellent !

Its an RSF 82 ET - it's actually 6 years old (installed feb 01)

cgoode said:

I The boiler is not noisy at all, and apart from the hot water problem it works fine.

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probly not sludge then. id say get a different eng back. one on recommendation ... or try british gas. peolple slate us on here...but we still in business. must be for some reason

That's what I thought too having read up on this and it seems the most common problem for sludge is kettling and radiator problems. The company I used was a local firm we've used in the past but he didn't seem too interested - probably because he was about to emigrate to Australia! I probably will call British Gas or similar .
Thanks. Enjoy your cooking and cleaning !!

Your model heats the water within the main heat exchanger and sludge is unlikely to be the cause in your particular case.

One possibility is that the pump is not running on DHW.

Obviously a competent boiler engineer would check the temperature sensors, flow rates and do a thermal survey to assist with diagnosing the cause of your problem.

Tony Glazier

Thanks for all your help.

Ring Ravenheat on 0113 252 7007 They can suggest a local approved installer who will probably carry the more likely parts with him.