Questions about Worcester Bosch Greenstar 37CDi combi boiler

18 Oct 2007
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United Kingdom
We moved house about eight weeks ago; the house has a WB37CDi combi boiler which is about 12 years old. Although the previous owners provided a Gas Safe Certificate, I decided to have the boiler serviced as, according to the service history in the Installation Manual, the last service was about nine years ago.

I employed the same GSR as my son (who lives nearby). He came with a young lad who did all the work (presumably a trainee as the Gas Safe website only lists the person I employed).

The service took about 15 minutes and consisted of attaching an analyser and taking some measurements. The results are as follows:

Operating Pressure 16.08 mB (I queried why it wasn't 20 mB, but he said it was OK.)
CO2% (High) 9.2
CO ppm (High) 63
CO/CO2 Ratio (High) 0.0006

No readings were taken at Low output.

Is this acceptable?

The condensate trap was not removed and cleaned; neither was the Magnaclean.

The Gas Safe man drew my attention to the cover containing the sight glass and said that there had been instances of the glass cracking and the boiler wiring being damaged (presumably by flames escaping). He suggested that the cover should be replaced by one without a sight glass (cost about £60). I queried why there had not been a recall.

Is there any truth in this? What would you suggest I do?
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Sounds like it Hasn’t really been serviced properly to be honest . The working pressure should technically be a minimum of 16.5mb at the appliance providing it’s a minimum of 19mb at the gas meter. Did you specify you wanted a SERVICE and not a safety check as safety checks usually just check pressures etc and not clean of condensate trap and filters ... the engineer is right about the sight glass and I would also recommend that it is replaced ( Worcester won’t repair for free as miles out of its warentee ) the max reading is just within the specified limits also. Readings MAY have been taking on the minimum rate some engineers record these readings and some dont
Your boiler has not been serviced, you have what is called a flue gas analyser check, or poke and go as we call them, sadly far too common and the people that do them wouldnt know how to do a proper service, all the large companies Bg, SSE and the likes are the cause of this fiasco, definately get the sight glass as you call it, correct name is electrode kit, comes without the sight glass,they are prone to cracking and can cause some expensive damage
That "service" was a waste of time...but even if you specified a safety check the following should have been advised given the time elapsed since a last full service (if ever done) and the unknown history.

In the interests of safety and efficient operation the following constitutes a full service...

Replacement of the top burner and front heat exchanger cover gaskets..they cook themselves over the years and will eventually fail and leak.
Replacement of the electrodes...the early ones have a sight glass that can crack and write off the boiler when combustion products incinerate the boiler. The electrodes also burn away over the years.
Replacement of the bearing plate (a rubber valve)....they can distintegrate
A thorough heat exchanger clean on the combustion side
A thorough condensate trap clean (I replace the seals too for what it costs)
Dropping the system pressure and checking/inflating the expansion vessel
Reseting the service indicator
Combustion checks (and likely adjustments) and a proper safety check of the installation (there are legal minimum requirements) etc
Other extras eg. replacing a leaking auto air vent

That lot will set you back £80 to £90 in parts and a couple of hours labour plus travelling....but you will get 15 to 20 years life and a safe boiler.

The idiots that turned up wanted an easy life and opted to do the least possible for a quick buck.
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Service procedure is in the manual. The above would certainly be an extremely thorough service and a lot of that work would be optional rather than required. All the cdis you can visually see if the condensate needs cleaning, the expansion vessel pressure will show if its required on the max combustion check. A clean of the heat exchanger fins depends on an acceptable fan pressure check. Seals need replacing every few years or if showing visual deterioration or distress. The magnacleans are really part of the system rather than the boiler, usually i would advise theres a good chance of the valves or seals leaking and that would cost extra time and materials but id be happy to do it if they accept that.
The fan pressure test is not particularly useful and not a great indicator in my experience, how can you possibly inspect the hex seals without removing the burner and front cover?
On the early traps you can't see if they need cleaning without stripping them down...there's a row of vertical holes between the chambers that gradually block with oxide.
So you stick it in FGA mode...get the rads red hot and then determine if the vessels low on pressure. That's just mad and masks a system with rads full of air. Apart from the fact that you'd normally FGA with the diverter pulled off and the DHW running.
Sounds like your not a fan of proper servicing.
Im not knocking your service, just saying its above and beyond what it needs. Obviously its 2 mi utes to whip out and clean the trap so you would...but you can see if they need doing.
I personally would do a full check on the vessel if rads need bleeding but i generally ask that first and if they do ill bleed them before testing emmissions. If the system can cope with it theres no need to run the tap.
The fan pressure test is as advised by worcester, they tell you the tolerances and with that the need to strip clean and replace seals.
Im not saying theres anything wrong with your service at all, just that the requirement is somewhere in between yours and the ops
Thank you, all repliers, for your comments. I definitely asked a Service and told the enginner that the boiler had not been serviced for over six years. I will get the electrode kit (aka sight glass) replaced by the same person.

As for future work/annual services, how do you find someone who can be trusted to do a job properly??? I haven't lived here long enough to ask the neighbours for recommendations; and manufacturers' "approved installers" appear to be connected more to how many boilers they sell rather than the quality of their work.
Hailsham, let the manual dictate what the service is, not the person called in and doing what he wants to do

Me thinks the guy is not familiar with the boiler
Hailsham, let the manual dictate what the service is, not the person called in and doing what he wants to do

Me thinks the guy is not familiar with the boiler
I agree with your first comment. However, he must have known enough about the boiler to know that the glass could crack and that the replacement part did not have any glass.
I agree with your first comment. However, he must have known enough about the boiler to know that the glass could crack and that the replacement part did not have any glass.
Glass thing is common knowledge
Manifold pressure is one of the checks the manual asks for
I was going to check the combustion figures but then that what is the point.
A flue gas check is not a boiler service any way you look at it
While that check tells you combustion process is acceptable, other service components may well be in poor health, a condition an analyser will never pick up
im sure with your thousands of comments in the past d hailsham you have read exactly what is required for a service in the worcester instructions and what it says is required if fan pressure etc is ok . .
IF you dont think the guy done a proper job why would you be having him back to fit the parts
All the poke and go service only brigade will be told about Technical bulletins at toolbox talks, doesnt make them engineers though
It needs to be cleaned out thoroughly, regardless. ( heat exchanger) wb do a full service for £120 . Local Worcester accredited engineers should be very thorough. Most are in my opinion. The trap needs cleaning and various other bits and bobs. It doesn’t sound a very thorough service,however, did you watch him all the time he was there? He may have done a lot more than you suggest?

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