Does my central heating need a Powerflush

asibs

Do I need a Powerflush?
I have a Glowworm 23C combi-boiler in my home, which is a terraced 2-bed property with 5 standard radiators and 1 bathroom radiator.


Short version
Symptoms are:
- boiler regularly goes into fault, on/off cycle or open/close of filling tap usually resolves
- boiler leaks underneath when the filling tap is opened to re-pressurise
- boiler overheat tripped twice in ~3 weeks
- radiators are in general cooler at the bottom (not cold - bottom is still hot to the touch, but not as hot as the top) - this was pointed out by the engineer, but I have checked and confirmed it is the case

Resolution:
- AA Home Emergency Engineer says to get a powerflush. Also says the filling tap may need replacing but I need to get a powerflush first...


Long Version
Shortly before Christmas the fault light began flashing. Unfortunately there's nothing new about this, it happens regularly over winter, I think it is usually caused by low pressure (the pressure bar is often between 0.5 and 1, when I believe it should really be in the 1.5 - 2.5 range). A simple off/on usually works, if not opening the filling tap then closing does the job - opening this valve has always (since I moved in) resulted in some water leaking out from under the boiler, which I've always been somewhat uneasy about, but my boiler services (provided by the AA) have never spotted it, and when I've pointed it out they've never seemed to think much of it...

Anyway, the fault light is flashing before Xmas, and the usual off/on and opening/closing the filling tap don't fix it. So I call out AA Home Emergency, he opens it up and says the overheat has tripped. He resets it and everything works fine again, but he recommends I get a powerflush.

I didn't do anything with the powerflush, I was going to look into it but the engineer didn't make it sound urgent at all and it was Christmas / New Year so I had other things to be doing.

So now, roughly 3 weeks later, exactly the same problem occurred. AA Home Emergency called out again, again the overheat has tripped. While looking at the system, the engineer notices the filling tap leak, which has been there for years and no other engineers have cared about, and says they may need to replace it, but as I've been recommended a powerflush I need to get that done before they repair anything else...

He also said the central heating was on full (5) and that I should set it lower (2.5 - 3) at least until the issue is sorted so it doesn't overheat again.


Question
I'm no expert, but I don't see how a powerflush is in any way related to the boiler overheating, or the filling tap leaking...? The only symptom it sounds like a powerflush would alleviate is the radiators being slightly cooler at the bottom - but they are still adequately hot and heat the property fine...

So do I need a powerflush, or are they just recommending this so they don't have to do anything else until I fork out hundreds of quid?

Rodney_Trotter

A power flush won't stop the leak.

southcoastrgi

it doesn't sound like it needs a powerflush but it needs the leak fixing which is prob why the pressure goes down & it overheats, it could also be an over senistive o/h stat

a question, when The AA come out are they in an AA van ?

asibs

Thanks, I was told on the phone when I booked the appointment that the last guy was an AA engineer. I'm not sure about the one ~3 weeks back though, I can't really remember whether it was an AA van or not.

The AA enginer this time pretty much just said "the last engineer said you needed a powerflush, so you should get one" without much justification...

And just to clarify, the leak is only when I open the filling tap under the boiler - I've never seen it drip otherwise. I do want to get it fixed, and have pointed it out to people servicing the boiler in the past, but I'm not sure whether that is really the root cause of the low pressure. I suppose it could be a slow leak and I've just never noticed any drips though...

[Edit] - Also, why would low pressure result in an overheat? Not saying you're wrong, but I wouldn't have thought one would cause the other (I'm probably totally wrong, but I'm curious!)

thegirlintheattic

Low pressure = not enough water in system = higher temperature.