Hot water cycling from hot to scalding to cold

[kepha]

Dear all,

I've just moved into an old house and have a central heating issue - hope you guys can offer some advice if possible please.

Problem: the hot water cycles from hot, very hot, cold, then hot again. This happens in all outlets but is particularly annoying when having a shower. I'm the only person in the house and not using any other applicances so I don't think it's an over-use issue (although I live in flats so I don't know if someone else is using the same mains feed). The boilers cycles on and off whilst this is happening.
I can solve this issue by having a hot tap running simultaneously - the hot water in the shower remains constant if I do this (it's the only way to have a shower at present).

Background: Worcester 28i rsf combi (GC 20 47 311 54). Not sure how old it is although there is a sticker on it stating the next service is due in 2003! There is a cold water tank which appears to still be attached - not sure why this is. I live in Edinburgh (soft water area).

Other issues:
Radiators: top half goes hot, bottom half only warm.

Question: What do you think the problem is? I was guessing it's either the thermostat in the boiler or the heat exchanger (if there's sludge in that then I guess that would also explain the radiators). Is there an easy way for a novice to distinguish between these issues? I'm not really competent to fix either of these issues - how much would a reasonable quote be (obviously depending on what the issue is)?

Thank you in advance.

 

[gas4you]

I would think the heat exchanger is blocked. It sounds from the description of your radiators that there is sludge in the system.

If the hot taps are running slow, it could be that the domestic side is scaled as well.

Best answer would be to have a powerflush and then if the problem still exists, replace the heat exchanger.

 

[bengasman]

Background: Worcester 28i rsf combi (GC 20 47 311 54). Not sure how old it is although there is a sticker on it stating the next service is due in 2003! There is a cold water tank which appears to still be attached - not sure why this is.

The wb i-series is a favourite model for cowboys, which explains why you still have a disgusting tank, when you could have had all mains; the installer probably just did a crap job.

 

[bengasman]

I would think the heat exchanger is blocked....

I doubt it Dave , it's an i
My guess is that the boiler does not modulate down, but cycles.