Faulty hot water sensor red herring?

1 Feb 2007
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United Kingdom

I've got a very frustrating Baxi 105e which seems to have a hot water sensor issue.

Every so often the hot water goes cold, then hot, then cold etc but it does not happen every time. When this happens you can hear the boiler ignite to heat the water then it cuts out and tries a few times before igniting again.

And on occasions the water stays cold, the dhw sensor led flashes and the boiler does not ignite. If you unplug the cable in the dhw sensor & plug it back in the light goes out and the boilers ignites again.

So all in all it's very frustrating!

Is it an issue with the dhw sensor, the cable that plugs in to the sensor or the circuit board?

I replaced the sensor about a year ago, it was fine for 6 months but now the issue is back. Was I just unlucky and got a dodgy sensor (cheap eBay one) or is the sensor a red herring?

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Could be none of the above

Is a common problem with many causes

Do you have the boiler serviced? ;)

How old is it? Was it fitted on an existing system? ;)
Yes, we have it serviced every year. It's being serviced on Friday.

The boiler is 9 years old but I'm not sure if it was on an existing system as it was here when we moved in. It's hard to tell.

So the boiler was serviced 2 weeks ago and all has been fine until this morning, it failed to ignite for the hw and the hw sensor led flashed. Quickly resolved by unplugging the sensor and reconnecting it.

The plumber said to change the air pressure switch if it happens again. When he serviced the boiler he blow down the APS pipes which seemed a temp solution.

Does anyone think replacing the APS might be worth a go?

What I don't understand why does un-connecting the hw sensor & reconnecting seem to work temporarily.

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Only a gas reg engineer should be touching the APS.

He should have measured the contact resistance but only a few seem to know how to do that!

The internal welds in the NTC can be faulty and go open circuit when hot.

Its most likely to be that which a DIYer can replace.

Moving the connector flexes the pins and can make it reconnect.


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