Glow-Worm 38cxi boiler

[ColdWaterRich]

Wonder if anyone can help me. I have a Glow-worm 38cxi boiler which was installed in Autumn 2005.

We have had some issues with water temperature over the course of the last few months.

The heating seems to work fine. The first problem was that when the hot water (for the shower) was turned on it became hotter and hotter and hotter until the boiler eventually cut out. (F14 fault which, according to GW's helpful! manual is central heating flow temperature more than 95C). Normal taps were okay although the heat of the water in those was not what it should have been.

Our plumber thought it was a diverter problem and changed that (to no avail). GW then indicated to him that there was a problem with some switching pin in the boiler which was changed yesterday. This has not solved the problem and having spoken to GW again, he has been informed that it is the heat-exchanger that needs replacing.

However, since the work yesterday the hot water is now almost non-existent. We can't get hot water to the shower at all and the boiler is cutting out (still F14) after about 5-10 seconds of the hot water tap being on (even though the boiler temp appears to be only about 65C ish)

I am not a plumber and have no knowledge about boilers or central heating but am becoming frustrated with GWs apparent lack of knowledge about their own system and our plumber's fruitless attempts to solve the problem.

In my own mind I can't understand why the heat exchanger would be a problem if the radiators are heating up fine but the water isn't. Maybe that is my lack of knowledge coming through.

Anyway I have seen other posts about GW boilers and they are less than complimentary but I am loathe to rip it out and start again when it is only 3 years old.

Any help would be greatly appreciated.

ColdWaterRich

 

[ColdWaterRich]

I should probably add that I think the plumber has changed the thermistor in the boiler too as he thought that was the problem originally.

Thanks

ColdWaterRich

 

[3continentsplumber]

I had a similar problem with a Britony boiler. Again replacing the thermistor did not help.
If there is gunge in the central heating circuit, some of it can find its way into the secondary heat exchanger that heats the hot water. The small water passages become blocked, obstructing the flow and causing it to overheat. The hot water then becomes hotter and hotter until the thermistor does its job and shuts the boiler down to prevent further damage.
What you need to do is to either flush out the secondary heat exchanger or to replace it and before you put the boiler back into operation, flush out the central heating system. This probably means a power flush and maybe fit a magnaclean filter to prevent reoccurrence. Sorry buts its not going to be a cheap solution.

 

[gas4you]

The heat exchanger they are refering to is the plate HE, not the main HE.

The plate HE heats the hot tap water using the system water thats flows around your radiators.

The DV sends the system water to either the system side of the plate HE, or the radiators.

It will be the system side of the plate that is blocked, hence no flow through it and the boiler over heating.

This needs taking off and cleaning, or replacing.

It sounds possibly as thought the boiler was fitted to a dirty system, and if this is not cleaned out, the plate will get blocked again.

 

[mickyg]

F14 = Plate heat exchanger, everytime, without fail.

to be honest, on any combi if you have hot water temp probs one of the first thing most good heating engineers will do is check this.