coozer
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| posted on 8/11/14 at 03:29 PM |
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Seasonal boiler problem?
Thought I would ask here first...
Seems its that time of year again and our Vokera boiler is acting up. After a couple of minutes in the shower the water cools off till its cold and
slowly warms up again.
I say seasonal problem but its not like we've changed anything, just shower and and hot water as usual.
Could it be the flow sensor dropping in and out? Had this before but the panel chucked a fault code at me and it was an easy fix.
Just hoping I'm going to be calling Helplink.....
1972 V8 Jago
1980 Z750
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coozer
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| posted on 8/11/14 at 03:48 PM |
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Just checked the hot water.
Turning the tap on lights the burner, the temp goes up to 46 and the flame goes out, it drops to 32 and comes back on. Back up to 46 and the cycle
continues.
Thermister?????
Steve
1972 V8 Jago
1980 Z750
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gingerprince
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| posted on 8/11/14 at 07:31 PM |
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I had similar symptoms on my Vokera combi. Turned out it was the DHW heat exchanger. Gets scaled up and then over heats and trips the stat until it
cools and starts again. Bit of a bit bitch to change apparently. I use a local Vokera specialist and the young lad always let's the old hand
do that job! It's not an unknown problem on these boilers.
[Edited on 8/11/14 by gingerprince]
[Edited on 8/11/14 by gingerprince]
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Bigheppy
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| posted on 8/11/14 at 08:29 PM |
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why replace the dhw heat exchanger. Its a few years since I was a service engineer in the heating industry but back then it was easy to descale the
dhw heat exchanger with brick acid/patio cleaner. Remove the heat exchanger from the boiler, fill with acid tip it from side to side and back to front
to expell all the air top up with acid, repeat until no more air comes out then leave it until it stops fizzing. Rinse and repeat. Refit and test.
Obviously consider health and safety precautions when using the acid.
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Smoking Frog
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| posted on 8/11/14 at 10:07 PM |
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quote:
Originally posted by Bigheppy
why replace the dhw heat exchanger. Its a few years since I was a service engineer in the heating industry but back then it was easy to descale the
dhw heat exchanger with brick acid/patio cleaner. Remove the heat exchanger from the boiler, fill with acid tip it from side to side and back to front
to expell all the air top up with acid, repeat until no more air comes out then leave it until it stops fizzing. Rinse and repeat. Refit and test.
Obviously consider health and safety precautions when using the acid.
But that would mean putting common sense before profit.
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cliftyhanger
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| posted on 9/11/14 at 07:30 AM |
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Looking from the other side, when a plumber down here charges £80 an hour, plus the fact they won't offer a warrenty etc, I can see why a
plumber would just replace the exchanger (I had one replaced on a vokera years ago, and fitted a magnaclean afterwards to help stop grot getting in
the boiler)
If doing yourself, I think descaling is a very good idea.....
incidently, a couple of years before the exchanger was swapped, the plumber reduced the gas pressure or something as a bodge to stop the cycling. That
worked, but had a knock on effect...
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joneh
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| posted on 9/11/14 at 08:39 AM |
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I had a similar issue with my condenser boiler. Turned out to be the pump was duff and not pushing the water around fast enough.
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gingerprince
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| posted on 9/11/14 at 09:11 AM |
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quote:
Originally posted by cliftyhanger
Looking from the other side, when a plumber down here charges £80 an hour, plus the fact they won't offer a warrenty etc, I can see why a
plumber would just replace the exchanger
Exactly. 10 year old+ part - if I'm paying someone to repair something, I'd rather them replace the part (which isn't that
expensive in the grand scheme of things) than fashion a fix that might need re-doing in a short period of time. If I were doing it myself then
I'd try the frugal option. But that would have probably been a balls-up because I wouldn't have paid someone to diagnose the issue and
would have "repaired" the wrong part 
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coozer
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| posted on 9/11/14 at 02:26 PM |
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Fixed it, fingers crossed!
After a look round some plumber forums and what not found a diagnostic test.
Turn the hot tap on and when the flame goes out at 46dc turn the tap off. Temp display switches to the main loop and displays the burner flow temp, in
my case it shot up to 92! That indicates a blocked heat exchanger.
Took the heat exchanger out and flushed loads of black scale out with brick acid as advised. Easy to see it was blocked as at the beginning it took a
while for the stuff to flow from one six to the other and the insides were black. After flushing the flow was much better and the inside shiny new
again!
Now the hot water is hotter than before, the temp stays steady at 49 now and the flame stays on, then turning the tap off the main loop temp is 70.
Let's see what happens next!
Thanks,
Steve
1972 V8 Jago
1980 Z750
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cliftyhanger
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| posted on 9/11/14 at 04:36 PM |
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Black scale is bits of rust stuff. Fit a magnaclean (or similar) they collect it all up for you.....really good bit of kit, especially on an older
system.
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perksy
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| posted on 9/11/14 at 06:23 PM |
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Sounds like your on the right track.
Was just about to suggest the heat exchanger myself as i've seen a few Worcester boilers do this aswell. Not an easy part to
remove but worth a try to save some cash.
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coozer
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| posted on 9/11/14 at 08:42 PM |
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Thing is over the years the system has been drained a few times and the water is always clean. Every time its been filled with inhiberter.
Will a magnaclean remove any of the limescale I suspect is built up round the rest of the system? Or, just stop the build up of any more??
Boiler is now 14 years old and going strong, had a few issues with it over the last couple years, its always around this time, and have always managed
to identify and fix it myself. Whole system was designed and installed by British Gas in 1999.
Previously had a Sonia Duval combi that soldiered on without any issues for 20 years! I even installed it myself!
And here's the rub.. I've never been robbed for a service in 35 years of combi ownership!
At the moment I'm loath to pay thousands for a new one while the scroungers get them for nowt!
1972 V8 Jago
1980 Z750
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cliftyhanger
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| posted on 10/11/14 at 07:14 AM |
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magnaclean won't touch limescale, but it will get all the black stuff, which are bits of rusty radiator.
When I had one fitted, I had to empty the magnaclean a few times in the first couple of weeks, it collected that much....(this was in a rental
house)
Flipside, on my new boiler install in my old house, the magnaclean collected very little over 8 years. However, that was a fresh install with plastic
pipework (not sure if that helps with electrolytic corrosion, as there are still bits of copper used) and new rads. Plus I put a definitely large
enough dose of fernox in there....
But for the £80 they cost, they can save a lot of hassle. And it seems they are often fitted with new boilers, not sure if it is a new regulation or
something.
If you want to descale the whole system, there is a fernox cleaner, comes in a buscket as powder, I think it is citric acid. On a combi, it will cause
pressure to build up in the system as gas is made in all the rads. So don't leave it!! And you will want a filter to catch all the crap
released. May not be worthwhile, as it could find weaknesses in the rads
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