Flate Plate Heat Exchanger for Gas combi boiler

square_bear

Hi
My hot water runs from hot to warm then back to hot again, this is especially noticeable when having a shower.

I am told by my gas engineer that it looks as though the flat plate heat exchanger may be faulty.

Is this a common fault, does it cost a lot to replace and what causes it to fail.

Thank you in advance for any help.

Ionkontrol

It happened to my dad's 18month old Worcester Bosch boiler. £250 to replace.

square_bear

Were the symptoms that I have mentioned the same for his boiler too?

George_Bray

square_bear wrote: »

I am told by my gas engineer that it looks as though the flat plate heat exchanger may be faulty.

Ask him why, in his opinion, it's faulty. Make sure he doesn't drill a hole in it, or damage it in some other way, to make sure it's faulty, before he answers.

A heat exchanger is very simple in concept. A house radiator or car radiator are heat exchangers. Fill a vessel like that with water or coolant, hang it over a burner, and that's roughly what going on in your boiler. What can go wrong and how likely is it? I'm no gas engineer but surely the main cause of failure would be a leak (water escaping) but how likely is that? Have you seen water escaping from anywhere? I guess it could get clogged up with cobwebs, flies, dust or carbon but that seems even less likely and it could be cleaned. I'm sceptical.

A leak seams unlikely if the heat comes and goes. It sounds more like a faulty sensor, an air bubble or something like that.

gas4you

Very common fault on combis. If no fault codes are showing when the water runs hot/cold then it will be full of muck on the system side of the plate.

It can either be taken off and cleaned with a acid based cleaner or replaced. Could be a sign that the system is full of sludge.

square_bear

George_Bray wrote: »

Ask him why, in his opinion, it's faulty. Make sure he doesn't drill a hole in it, or damage it in some other way, to make sure it's faulty, before he answers.

A heat exchanger is very simple in concept. A house radiator or car radiator are heat exchangers. Fill a vessel like that with water or coolant, hang it over a burner, and that's roughly what going on in your boiler. What can go wrong and how likely is it? I'm no gas engineer but surely the main cause of failure would be a leak (water escaping) but how likely is that? Have you seen water escaping from anywhere? I guess it could get clogged up with cobwebs, flies, dust or carbon but that seems even less likely and it could be cleaned. I'm sceptical.

A leak seams unlikely if the heat comes and goes. It sounds more like a faulty sensor, an air bubble or something like that.

I completely trust his opinion on what the problem may be.

His assessment is based on what I have told him is happening when the shower is running.

He said that althouth I am still getting hot water, a little build up of scale may be causing the problem.

square_bear

gas4you wrote: »

Very common fault on combis. If no fault codes are showing when the water runs hot/cold then it will be full of muck on the system side of the plate.

It can either be taken off and cleaned with a acid based cleaner or replaced. Could be a sign that the system is full of sludge.

I have a Baxi Combi 80e.

I will have a look in the manual for the fault codes. Thanks.

Is it an easy job to take off the exchanger and clean it?
I am quite handy when it comes to jobs like this.

macman

So he's given this diagnosis without actually examining the boiler?
Is the boiler still firing when the flow goes cold, or does the burner cut in and out?
If the latter, then it might be the diverter valve.

C_Mababejive

If the H/Exch was blocked,why would it be hot sometimes and cold another time? Are we saying that the burner is modulating or going on and off?

George_Bray

square_bear wrote: »

He said that althouth I am still getting hot water, a little build up of scale may be causing the problem.

If it's scale, then ask him why he allowed hard water inside that system, assuming it was the same chap. It's asking for trouble.

gas4you

C_Mababejive wrote: »

If the H/Exch was blocked,why would it be hot sometimes and cold another time? Are we saying that the burner is modulating or going on and off?

If the plate HE is full of muck on the system side, then the boiler cannot transfer the heat quick enough to the domestic side. The sensors detect the system side water is too hot, so shut the boiler off. Boiler cools and repeats the process.

Boiler controls assume they are doing their job properly so no fault codes shown.

If it was the domestic side of the plate scaled up, then you would normally, but not always, get an overheat fault code.