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Frustratingly, this Baxi 100 HE boiler only locked out intermittently, making it difficult to find the fault. Only when the lock-out problem became more frequent were we able to pin it down.
We rang the Baxi Technical help line in 08706 049049. Another number for the Baxi Potterton help line is 08706 060955. They suggested that this could be caused by a problem with the old-style condensate trap.
It's easy to determine which condensate trap is fitted, and this applies to the Baxi Barcelona boiler too, which used the same condensate trap. The earlier trap is much shorter than the new trap, only about half the height of the available gap at the bottom of the boiler. The photo to the right shows the condensate trap (sometimes called the condense trap) to the left of the fan. That's an old condensate trap. The new trap is half as tall again.
As a safety mechanism, to prove that the condensate pipework has not become blocked, two electrical terminals are fitted into a "well" on the top of the condensate trap. A connection from the flame rectification circuit is made to one terminal and the other terminal is connected to earth. If the condensate drain pipe or the trap become blocked, a small hole in the bottom of the well allows condensate to pass up into the well, making an electrical connection between the contacts, allowing the flame rectification current to leak to earth. This shuts the boiler down.
The problem occurs when moisture or contamination between the terminals is present even when there is no blockage in the condensate trap or pipework. This causes the boiler to lock out. The new trap is much taller, keeping the electrical terminals further from the condensate. The well on top of the trap is deeper and the hole through which the condensate passes into the well is much smaller. This keeps the area between the electrical contacts drier and cleaner, helping to prevent nuisance leakage of the flame rectification current to earth. The small hole is visible directly below the right hand electrical contact in the photo below.
If your Baxi 100 HE boiler (or your Baxi Barcelona boiler) keeps locking out, first check if the condensate trap is over-full. If the condensate waste pipe is blocked or frozen, or if the trap itself is blocked, the trap won't be able to empty and this will be correctly shutting the boiler down.
If the trap and condensate pipe are not blocked or frozen, try temporarily disconnecting either the earthing lead from the trap or the white lead (making sure the white lead does not earth out). Try running the boiler with the lead disconnected. If the boiler runs correctly try re-connecting the lead.
We disconnected the lead and the boiler ran normally. With the lead re-connected the boiler locked out. We repeated this process to be sure. The Baxi 100 HE boiler locked out each time the lead was re-connected but not with it disconnected.
We fitted a replacement, new-style, condensate trap. It's a bit of a tight fit but we followed the instructions that came with it and it worked. It's important to fit the black screwed connection to the boiler sump before connecting to the condensate trap. If you connect it to the trap first it becomes very difficult to connect the black screwed connection without cross-threading it.
With new new condensate trap fitted the boiler worked perfectly. This should also apply to the Baxi Barcelona boiler, which used the same "early" condensate trap and which will accept the new condensate trap.
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The information provided on this web site is given in good faith and is only an indication of what we have tried in an effort to resolve heating and boiler problems. You must make your own judgements and we can accept no liability for any damage or injury sustained as a result of trying what we have tried, nor can we accept any liability arising out of misleading, incomplete or incorrect information on this site.
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We have also started to put together a guide to shower types, gravity showers and power showers. You can find it at powershowerguide.com
It’s possible that fault-finding may not sort out your problems or that the repair costs mean you should consider having your Baxi boiler replaced. For a replacement boiler or a new boiler installation we would recommend Worcester Bosch. Given current regulations and the work involved, boiler replacement is never cheap but sometimes a new boiler installation is the best option.
Why are Worcester Bosch our first choice for boiler replacement?
Worcester boilers are well made and the quality seems consistently high. Their technical backup is very good. The warranties on Worcester boilers are good and we’ve found that Worcester spares are readily when needed. We hardly ever have to wait long for spares.