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Topic Title: Off topic, Worcester Bosh condensing boiler
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Created On: 04 March 2013 06:57 AM
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 04 March 2013 06:57 AM
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deapea

Posts: 370
Joined: 13 May 2007

I know this is off topic but was hoping someone might be able to help.

I have Worcester Bosch Greenstar 28i condensing boiler and starting having problems with it last night. From cold, heating and hot water work ok but after a short period of time the boiler shuts off but no fault lights are displayed and pressure gauge reads ok. I have a feeling that the heat exchanger is going over temp. I've removed front cover from boiler and the heat exchanger gets extremely hot in a short space of time, there is a thermistor on the top of this and this is what I suspect is shutting the boiler down.

So I'm thinking that the water isn't leaving the heat exchager quick enough and maybe a problem with the pump or divertor valve. But these must be working as HW and CH work for a while from cold, rads get warm so heat is leaving the boiler.

Anyone had similar problems and got suggestions on what might be causing this?

Many thanks in advance.
 04 March 2013 07:45 AM
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alanblaby

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It wont be the divertor valve, unless it is absolutely filthy and gunged up, which is unlikely. With a divertor valve, this is a combi boiler then?

Does the heating work well with the temperature turned right down on the boiler internal stat?
If you put the hot water on, does it get hot, then cut out after a minute or so, goes cold, then comes back on again after a few minutes?
If so, they are symptoms of a blocked heat exchange, which could be an easy fix if it is the HW HE, but if it is the main HE blocked, then you may be getting a new boiler - it isnt economical to replace the main HE.

Could be the pump. Is the heating working at the farthest rads, if only for a few minutes? If so, the pump is working.
How old is it? 5 years and older it may have some blocked fins/runs in the heat exchanger, thus causing this problem. What colour is the radiator water if you drain one off? Totally black with rust particles will show the heat exchanger is likely to be partially blocked. If it is pretty clear (the installer has put inhibitor in it), then it is unlikely to be a blocked HE.
A little more info needed to narrow it down.
 04 March 2013 09:02 AM
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deapea

Posts: 370
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Originally posted by: alanblaby

It wont be the divertor valve, unless it is absolutely filthy and gunged up, which is unlikely. With a divertor valve, this is a combi boiler then?



Does the heating work well with the temperature turned right down on the boiler internal stat?

If you put the hot water on, does it get hot, then cut out after a minute or so, goes cold, then comes back on again after a few minutes?

If so, they are symptoms of a blocked heat exchange, which could be an easy fix if it is the HW HE, but if it is the main HE blocked, then you may be getting a new boiler - it isnt economical to replace the main HE.



Could be the pump. Is the heating working at the farthest rads, if only for a few minutes? If so, the pump is working.

How old is it? 5 years and older it may have some blocked fins/runs in the heat exchanger, thus causing this problem. What colour is the radiator water if you drain one off? Totally black with rust particles will show the heat exchanger is likely to be partially blocked. If it is pretty clear (the installer has put inhibitor in it), then it is unlikely to be a blocked HE.

A little more info needed to narrow it down.


Thanks for the reply Alan. I'm at home today so I'll check the things you have suggested and report back.
The boiler is about 3 years old in a Worcester Bosch Greenstar Junior 28i.
The water runs clear from drain points.
Just cleaned the syphon trap, quite a bit of dark sandy residue but first time this has been cleaned.
About a month ago I had a problem with the PRV blowing. When I tried to top up system the PRV dumped straight to drain, must of damaged diaphragm when it first operated. This looked a bit of a pig to replace so I fitted an inline 3 bar PRV. Suspect this fault could of been due to flat air bag in expansion vessel so I checked this as well. This was flat so I re inflated. There was no water coming out when centre pin of valve pressed so I think the bag is intact.
All has been working fine until yesterday. Could the old fault from a month ago be related to this new one or do things in general start failing after 3 years on these boilers?

Cheers.
 04 March 2013 10:13 AM
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deapea

Posts: 370
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Originally posted by: alanblaby

It wont be the divertor valve, unless it is absolutely filthy and gunged up, which is unlikely. With a divertor valve, this is a combi boiler then?


Does the heating work well with the temperature turned right down on the boiler internal stat?
Just tried this and it worked ok for about 10 mins and all rads stared to heat up then HE got very hot and green flame LED went out.

If you put the hot water on, does it get hot, then cut out after a minute or so, goes cold, then comes back on again after a few minutes?
Hot water works for a very short period of time and then HE gets very hot and green flame LED goes out. There are then some worrying banging noises from the boiler, also a sound like steam from the HE.

Having said that sometimes the hot water works fine???


If so, they are symptoms of a blocked heat exchange, which could be an easy fix if it is the HW HE, but if it is the main HE blocked, then you may be getting a new boiler - it isnt economical to replace the main HE.

Could be the pump. Is the heating working at the farthest rads, if only for a few minutes? If so, the pump is working.

 04 March 2013 05:35 PM
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alanblaby

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The first port of call would be the DHW heat exchanger.If that is gunged up, the flow rate will not be enough to over-heating.
Clean it out, see if that makes a difference.
Or, could be the main heat exchanger, but at 3 years old, it would be really rare for that to get blocked in such a short time.
PRV / pressure - I dont think they will have any effect on what you are experiencing, apart from if the pressure is too high, and heating the water takes it over the high limit.
I thought they had 5 years warranty?
 04 March 2013 05:38 PM
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AJJewsbury

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From cold, heating and hot water work ok but after a short period of time the boiler shuts off but no fault lights are displayed and pressure gauge reads ok.

We had similar symptoms from a Greenstar system boiler a winter or two ago - turned out the condensate pipe had frozen. I guess a blocked pipe or syphon might have the same effect.

- Andy.
 04 March 2013 06:44 PM
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DOUGIE1000

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I would do a hot flush several times and also fit a tf1 or magnaclean as could be something like poor flow problems.

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 04 March 2013 07:04 PM
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davidwalker2

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Worcester Bosch have a really helpful technical department, the number should be in the handbook/instructions.

David
 04 March 2013 07:07 PM
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DOUGIE1000

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valiant that want your card details before your passed over to technical adviser,

They charge for technical help, think its a £5 a cal

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 04 March 2013 07:32 PM
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deapea

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Originally posted by: davidwalker2
Worcester Bosch have a really helpful technical department, the number should be in the handbook/instructions.
David


I phoned the tech support line and to fair the were very good. I chose the option as a customer not an installer but when I explained to the young lady that I was an electrician she put me through to technical support for installers.
I explained the symptons to the guy and he agreed with what I thought, the water is not getting away from the HE quick enough hence causing an overtemp of the HE. His list pof suspects were:
1.Pump
2. Restriction to flow somewhere
3. Airlock.

I don't think its an airlock as I've bled all rads and tried the manual vent at the top of the HE (no air present).

Not so sure about the pump as when first tried from cold all rads do start to warm up. His response was that its a bit like driving across town in traffic, you'll get there but will it be quick enough?

That leaves with thinking restriction to flow and my guess would be HE blockage, I've read that it doesn't take much to cause this. I had a rad off today and connected garden hose to give it a flush out expecting to see sludge but it was reasonable clear. Also when I drain the system it runs clear. The Worcester Bosch guy had a good analogy for this as well, if a person's arteries were clogged up with collestral and you cut their thumb you would get a nice clean flow of blood.

Its a case of spend a fair amount of cash on trying to guess the faulty part or buy a new boiler. Very frustrating !!!!
 04 March 2013 07:45 PM
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OMS

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Flush, with any reasonable pressure from the MCWS, the guts of the DHWS heat exchanger alone - not a gauranteed result as often the scaling is from insoluble carbonates in your CWS - so water pressure alone won't shift it - it will give you a clue however as to what's inside there - you can get a replacement DWS heat exchanger fairly reasonably.

From all the symptoms you describe I'd be pretty sure it's a scaling problem in the heat exchanger - but your previous history of blowing a 3 bar PRV and the the "collapse" in the expansion vessel are likley to be related

Regards

OMS

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 10 March 2013 09:26 PM
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andrew331

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I hope you have been able to solve this now.

last autumn I tried our heating after it had been switched off for months and had a simillar problem. I would turn the heat on, the bolier would light, radiators start to get hot, the boiler would get very hot and then shut itself down. A plumber fitted a new pump which did not help, diagnosed it as a flow restriction and recommended power flushing.

In a desperate attempt to avoid the cost of power flushing I drained and flushed repeatadly using a hose pipe connected from the mains to the radiator pipework and eventually got it working. It took me about two half days to do it but it has got us through the winter so far.

Apparently modern combi boilers are very easliy blocked.
 10 March 2013 09:39 PM
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hertzal123

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On the subject of technical help lines,I have noticed that some tech lines will not give help without a gas safe reg number,which seems unreasonable for a purely electrical fault.Anybody else had this problem?
Regards,
Hz.
 10 March 2013 10:40 PM
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AncientMariner

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Unless they have changed their policy, Worcester Bosch have a fixed price repair service. Basically two prices depending on whether the heat exchanger has failed or not.

I used this a few years ago for our WB boiler and was happy with the overall service and cost. Signed up to their annual fee afterwards and to be fair have had more parts fitted than paid for; until one rather grumpy engineer identified the main problem: no expansion vessel in the COLD feed. This requirement is in the Installation Manual but usually ignored by installers, even WB registered ones. Basically a water meter acts as a NR valve and each heating cycle causes overpressure. With our boiler this resulted in blowing joints which due internal location within boiler are time consuming to fix, plus their policy seems to be to replace the whole module and not just the 'o'ring. The original problem, no hot water, was a seized diverter valve. Boiler was about 5 years old with Fernox from day one.

Cheers!

Clive

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 10 March 2013 11:27 PM
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M.Joshi

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Is it the newer Greenstar 28i Junior? If you can obtain/borrow a flow (Wier) cup, measure the flow rate of the hot water from a single hot water tap opened fully.

Assuming you have the 2009 - 2011 revision boiler, the hot water flow rate should be 10 litres/minute.

If it is less, there is most likely a blockage in the turbine or scaled up plate heat exchanger as others have mentioned above. That boiler is a pain to work on as the whole hydraulic block has to be removed to access the plate heat exchanger.

I think the turbine is easier to access - you can download the installers/service manual from the Worcester-Bosch website which shows you how to dismantle it.

Flushing the central heating (radiator side) will not clear the blockage.

I think Worcester-Bosch now charge close to £300 for a one-off call out to repair any fault - or you can go for their annual plan which is slightly more. If it is the plate heat exchanger, you will most likely end up paying more than the Worcester-Bosch one-off charge to a local independent company.

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 12 March 2013 10:33 PM
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antric2

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Originally posted by: hertzal123

On the subject of technical help lines,I have noticed that some tech lines will not give help without a gas safe reg number,which seems unreasonable for a purely electrical fault.Anybody else had this problem?

Regards,

Hz.




Yes, Vaillant were so jobsworth when one of our customers had a630 and 618 installed that i could not get to the bottom of an electrical problem with one of the boilers and the third party equipment the customer had bought to attach to the boilers.

They said they would only speak to me if i was a registered installer despite the fact there registered engineer came and couldnt work his laptop.
It was a nightmare and in the end between myself,the customer and the plumber we sorted the situation out.
Regards
Antric
 16 April 2013 12:08 PM
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tomgunn

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I personally wouldn't recommend doing a pressure clean of any boiler - it, in my opinion, would cause more trouble than its worth - I feel it just pushes the dirt into places you wouldn't want it to go and they charge too much for this too! I use a solution 200 / 300 and then flush after a few weeks.

Tom

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 16 April 2013 09:56 PM
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Grumpy

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Just come out of hibernation Tom?
 16 April 2013 10:04 PM
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stateit

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Well, the weather's the same as early March isn't it ?!

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 16 April 2013 10:30 PM
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Martynduerden

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Have you fixed it?

Likely causes

Blocked Plate heat exchanger
Faulty flow switch
Faulty dhw temp sensor
Faulty pcb - unlikely
Slow fan

Can you check the fan pressure?

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