Power flush ?

Inigo_Montoya

We have been having problems with our combi boiler for a while now

It started with the mixer shower going from hot to cold then back to hot - we got a plumber to clean the the boiler heat exchanger but that did not solve the issue - then a valiant boiler engineer who came out said we needed a new boiler as trying the fix it was not economical

Just a couple of days ago the boiler started banging loudly & quite alarmingly - this stopped when we toggled the heating off & then back on from the control panel

Apparently the banging could be caused by sludge build up in the system causing a blockage in the boiler which then causes the water being heated in the boiler to boil off, turning to steam & resulting in the banging noise

As such before resorting to buying a new boiler we are considering getting a power flush

Does anybody have any advice as to whether this is a good idea & if so how to get someone in who knows what they are doing & wont rip us off on price ? - what is a reasonable price for a large house with about 15 radiators ?

NSG666

What did the Vaillant guy say the problem was? If the problem is sludge then fitting a new boiler is just going to mean that you have a new boiler that fails due to sludge that is not covered by warranty.

Did the plumber who cleaned the heat exchanger fit a magnetic filter into the circuit? Would have been a very good idea as a means of trying to remove any sludge before it got to the heat exchanger.
If the HE was blocked, did he suggest at least draining the system to remove some of the sludgy water?

Bendy_House

The initial symptoms are of a P2P exchanger being blocked by sludge - I should know... 
Banging, too, can be caused by this; anything that prevents the heated water from the boiler flowing out as it should. A sticking diverter valve, for example (ditto... :-(    )
IF you problems are down to sludge, then a power-flush should be on the cards in any case, should you replace the boiler, so expect one to be required whatevs you decide.
So that leaves - is it worth doing one NOW to try and 'fix' your existing boiler? Hmmm, only if the boiler is young enough and worth keeping on. If, say, your boiler also needs a new P2P (£100+), a new diverter (£140+), and possibly more, is it still worth it? I don't know.
That's a large house, so expect a PF to be £600ish? As part of a new boiler fit, it could be less.
I think I'd first want to know IF the issue is sludge - do you have a magnetic filter fitted? If so, what has it caught? Or, are you able to remove a downstairs rad and take it outside to flush it through, and see what comes out?
How old is your boiler?

Inigo_Montoya

to answer some of the above questions :

this was a while ago now but IIRC the valiant engineer, like out local plumber, also thought it was likely to be a problem with a blocked heat exchanger due to the error code(s) on the control panel but that it would not be economical to replace it - dont recall either of them mentioning a possible problem with the diverter valve

IIRC neither the plumber or the engineer mentioned sludge in the system as a root cause of the blockage - I only discovered that possibility via my own research

the boiler is about 12 to 13 years old so I assume it will probably need replacing fairly soon anyway - it has been serviced once a  year since it was installed

I do not think we have a magnetic filter fitted so cannot do that check - also not sure i want to mess about removing a radiator when I am fairlycertain the issue is sludge already - when you put the rad back how do you prevent airlocks ?

The house itself is around 40 years old with its original radiators which is another reason I think that sludge is the likely issue i.e. older radiators more likely to corrode ? (the last power flush would have been when the boiler was installed)

Do people think we should replace the radiators since they are so old ?

If a flush is going to cost circa £600 then my thinking is just to go for a new boiler now with a power flush included as part of the install

Finally another factor is that its the boiler at my elderly (but spritely) mothers house (shes 78) so a new boiler installed now might even outlive her 

Any advice on getting a new boiler ? - when I started looking into this a while ago we were looking at the following brands Intergas,  Worcester Bosh, Vaillent & Veismann 

Bendy_House

I agree - at 12+ years old, it would be false economy to try and fix it.

And, yes, an included power-flush should be cheaper than a separate one.

Your system will be 'sealed' (unvented) - it'll have a pressure gauge? A sealed system should generally be less likely to suffer from internal corrosion. Mind you, none of them should, as inhibitor should be added, and rechecked every few years...

I'm guessing that the 'exchanger' the plumber mentioned is the 'secondary' one, (the 'plate-to-plate') and not the 'main' one which is where the burner is, since the symptoms - water fluctuating hot and cold - is a classic blocked P2P one. A stick diverter valve can also cause this as it doesn't open fully to allow the boiler water to get in to the P2P, so - again - can make the boiler 'cycle'.

Anyhoo, I think the decision has been made? In which case make it clear to all who come out to quote that you suspect a shed-load of sludge

Whether to replace the rads too? That's tricky, since if they are still solid, then it would be false economy, and MSE is all about saving money. However, if they are genuinely badly corroded inside, then their walls will be thin and their life expectancy reduced. It can even happen that a power-flush makes them leak, as sometimes it's only the layer of sludge which is blocking pinholes!

Perhaps ask each plumber their opinion? Or, go around each one and check along the bottoms of the rads, look and feel for 'bubbles' in the paintwork.

NB: If you do decide to replace any, especially the 'main' ones in the living areas, then seriously consider up-sizing them. Eg, go for versions with an extra panel or additional fins, or even slightly larger. If you do this, you should be able to get the same heat out of them as before, but at a lower water temperature. The lower the temp you can run your new boiler, the more efficient it will be = energy savings.

As for make, I dunno. I do love the sound of the Intergas, and they should have been in this country long enough now to have proved themselves (if they are as good as claimed), so worth some research. Veismann also rated highly, I understand, but all these should be good.

Belenus

Bendy_House said:

NB: If you do decide to replace any, especially the 'main' ones in the living areas, then seriously consider up-sizing them. Eg, go for versions with an extra panel or additional fins, or even slightly larger. If you do this, you should be able to get the same heat out of them as before, but at a lower water temperature. The lower the temp you can run your new boiler, the more efficient it will be = energy savings.

I have little knowledge of boilers but I have read on here that condensing boilers only operate in the more efficient condensing mode above a certain temperature.

Is that correct and how does that affect the bit in bold?

Bendy_House

Belenus said:

Bendy_House said:

NB: If you do decide to replace any, especially the 'main' ones in the living areas, then seriously consider up-sizing them. Eg, go for versions with an extra panel or additional fins, or even slightly larger. If you do this, you should be able to get the same heat out of them as before, but at a lower water temperature. The lower the temp you can run your new boiler, the more efficient it will be = energy savings.

I have little knowledge of boilers but I have read on here that condensing boilers only operate in the more efficient condensing mode above a certain temperature.

Is that correct and how does that affect the bit in bold?

In essence, the cooler the return flow, the more heat it can extract from the flue gases. 
A boiler could already be running in 'full' condensing mode with the rads originally installed for a conventional boiler, but chances are it's unlikely, especially in winter.
Also likely that, to get your rooms up to temp as quickly as with the original boiler, you'll have to crank up your condensing boiler's flow to a point where the return will only be partially condensing. 
Anyone contemplating replacing their rads should investigate this, and get proper advice on it.
With future heat/energy sources such as heat pumps, solar, etc, a thing they have in common is a low temp. 
UFH is, I understand, the best outputting system for this reason.

Inigo_Montoya

According to my mother the mixer shower has now started working properly again (i.e. not going hot - cold - hot)

I suspect the load banging from the boiler may have actually had a beneficial effect of clearing a blockage in the heat exchanger

Hopefully the shower (& boiler) will keep working till we get the boiler replaced