Vokera Linea 24 Boiler Issue, Advice Required Homeserve prob

[PlumbPunter]

Hello Forum,

I am hoping some of you fine professionals can offer me some friendly advice.

Ok, so I have boiler cover with Homeserve. Had issues with them before trying to claim my boiler was a 'beyond economic repair' when all that was required a was £90 part, which was resolved after eventually speaking to a director, and not being fobbed off.

I have a new issue, The hot water on my Vokera Linea 24 is intermittent, IE: When running hot water, it goes cold, then hot, then cold, etc. etc.

So I called Homeserve, they sent the subcontracted engineer who seemed clueless; so I mentioned I had researched the problem on the net, and it was suggested the 'primary thermistor' could be the issue.

Anyway, the same Homeserve subcontractor comes back today and replaces:

a) Primary thermistor
b) DHW Thermistor.

The issue is STILL there, cold, then hot, then cold, then hot.

So the Homeserve guy say's "Well, you must have limescale in the plate to the heat-exchanger, and your Homeserve insurance 'does not cover it".

Hmmmm. This is why I have come here today, to ask your professional opinion.

A few facts:

1) The central heating works fine

2) The hot water goes from hot, to cold, to hot, to cold.

BUT, and this is what caught my attention:

I timed the distance between the burners going on (hot water coming through), and going off (cold water coming through), when running the hot water consistently.

The times are EXACTLY the same between burners on, and then burners going off. Like this:

1) Turn hot water tap on.

a) Burners run for exactly 30 seconds - producing hot water.
b) Burners then turn off for exactly 12 seconds - producing cold water.

And the above times are repeat identically until the water tap is turned off, therefore repeating the cycle of cold, hot, cold, hot, with the burner times being totally consistent.

I would appreciate your thoughts on this, and I would absolutely appreciate your comments as to what the cause is, or whether the Homeserve guy is fobbing me off, due to lack of know-how, before I contact them to dispute their 'diagnosis'.

Thank you in advance

 

[45yearsagasman]

Plate heat exchanger may well be restricted. This is a very basic check to make with those symptoms. You have employed a parts chucker.

 

[PlumbPunter]

Thanks for the reply.

Plate restricted? Is that the same as limescale on the plate to the heat exchanger?

I just find it strange that the time differences between the burner firing and going off again, being exact every time.

 

[Tinitus]

If you open a hot tap fully and read the temperature it reads with hot water tap running, try to establish what temperature it reads as it cuts out. then do the same again but just before it cuts out close the hot tap and read the temperature again, if the boiler is not near a hot tap you may need someone to help read the temperatures. Put the temperature readings on here and I can tell you if the plate heat exchanger is blocked.

Paul

 

[Agile]

What you have described are the classic symptoms of a blocked plate heat exchanger.

Amusingly, they employ such muppets who cannot diagnose even the most basic and common of faults. You apparently persuaded one of their muppets, who obviously did not know any better, to change parts which were not the cause and in any case could have been measured to see if they were faulty.

What are you going to do now?

Tony

 

[PlumbPunter]

What am I going to do now?

I have no idea, Homeserve said it is not not covered

A blocked plate heat exchanger? How is that fixed?

 

[libby lou lou]

Yoy can't do it, youv'e asked too many questions for a simple repair

 

[PlumbPunter]

Just doing a quick check. Am I right in thinking that THIS is what needs to be changed and fitted to fix this problem:

http://www.ezypart.co.uk/parts/part_id__2078

?

Thanks.

 

[dcawkwell]

Sounds like you have sludge and rust throughout your central heating system and that has come around and blocked the hot water plate heat exchanger.
Limescale would reduce your hot water to a trickle.

Homeserve won't cover you for this.

Maybe you can get one of the boiler super heros off this forum in
the London area to sort you out.

Some will say it need a powerflush. My quicker dirtier preference
would be to mains flush the central heating a bit and remove
and flush the DHW plate heat exchanger.

 

[Agile]

Unfortunately the Homeserve nupties dont know anything about chemistry and think that the blockage is "limescale".

It can be limescale in a hard water area like Buxton or Bracknell. But that creates a different symptom. In the extreme it can block all or most of the DHW flow.

The reality is that in the London area the water is not very hard and limescale problems are rare and only present when there is another fault such as a dripping hot tap.

In almost all cases, the blockage is caused by iron oxide based sludge. Thats from the heating system and consideration needs to be given to what treatment may be necessary to reduce the chance of it occuring again very soon.

There are also other parts of the boiler which need to be checked when the plate HE is replaced or cleaned.

Tony