Baxi 80e Combi Boiler Woes

[migrantwing]

Living in rented accomodation for 3 years. Had a few issues with the boiler (Baxi 80e). The water pressure has been dropping a lot, down to around 0.5 bar. Came to run a bath last night and noticed a flashing light. The error, according to the manual is an 'Error on Hot Water sensor'. I have looked online and someone suggested that it is the hot water thermistor and after searching, have found a replacement part for around £5 (photo below).

My question is; can I buy and fit this part myself (comptent person) or does it need to be a certified boiler engineer that needs to carry out the replacement/repair?

I actually think that a new boiler is needed, at the very least a good few £'s of repairs, but our landlord is more of a friend than a rich property developer, so is not made of money. He only rents out this property to us, otherwise he works a full time job. It's more of a 'we're helping him, he's helping us' kind of rental agreement, although we do have a formal agreement contract.

Thanks in advance.

 

[gas112]

good boiler and simple ten minute fix there is nothing on this boiler that cant really be fixed without being expensive

 

[bernardgreen]

but I don't think our landlord is made of money.

That doesn't matter, he or she has a legal obligation to provide and maintain the heating and hot water appliances at his or her expense.

The thermistors resistance is "read" by circuitry in the control system ( aka the PCB ) and that circuitry may be at fault and the thermistor is not faulty.

Other s can comment on the "legality" of a tenant tampering with the landlord's gas appliances.

 

[migrantwing]

good boiler and simple ten minute fix there is nothing on this boiler that cant really be fixed without being expensive

Sounds like good news. I know it's getting on in age, but it's done the job thus far. I'll phone my landlord and see what he says.

 

[migrantwing]

but I don't think our landlord is made of money.

That doesn't matter, he or she has a legal obligation to provide and maintain the heating and hot water appliances at his or her expense.

The thermistors resistance is "read" by circuitry in the control system ( aka the PCB ) and that circuitry may be at fault and the thermistor is not faulty.

Other s can comment on the "legality" of a tenant tampering with the landlord's gas appliances.

He has no problem fixing things, we had to have a new PRV fitted last year. I was just trying to fix it myself, but then read your comment about the PCB, so who knows? Plus the fact that if a new boiler is required (at £2000+) it will reflect in an increase in our monthly rent

 

[migrantwing]

May I add that the central heating is working, but not the DHW to the taps.

 

[gas112]

There is 2 stats before this one that control the boiler

 

[migrantwing]

@gas112 sent you a PM

 

[ollski]

If the 70 degree light is flashing you need to test the resistance of the sensor. between 1 - 30 kohms it will be the pcb, outside that the sensor, but at 5 quid you don't have much to lose by sticking it on.

 

[migrantwing]

If the 70 degree light is flashing you need to test the resistance of the sensor. between 1 - 30 kohms it will be the pcb, outside that the sensor, but at 5 quid you don't have much to lose by sticking it on.

Yeah, that's the one, the 70 degree light flashing.

Got someone coming around to look at it, a friend of a friend who is friends with my landlord and a gas fitter. Boiler probably needs a service and a few repairs. Shame as I'd like to have had a go myself. Plus the fact I don't have a multimeter

 

[Agile]

Whilst a competent DIYer can do a lot of things to a boiler, that should really be someone who has a meter and knows how to use it properly.

Some things which are gas, combustion and safety aspects should only be done by a professional.

Your Landlord should also have gas safety certificates done each year.

Tony

 

[bernardgreen]

between 1 - 30 kohms it will be the pcb

that is a very wide range of acceptable values of resistance,

A typical temperature sensing thermistor would be about 5 KΩ at 0°C and 2.9KΩ at 100°C

That said the one used in the boiler may be a very different type.

It would sensible to obtain a copy of the temperature / resistance graph for the type used in the boiler and use that to verify the thermistor is within the acceptable tolerance.

The thermistor circuit on the PCB could be tested using known resistors to replace the thermistor and thus simulate the thermistor being at various temperatures and verify that the control / indications are correct for those simulated temperatures.

 

[Agile]

But I only change what needs to be changed.

Regardless, measuring an NTC takes about 60 seconds unless its a Heatline if you don't have a spare plud connector.

Tony

 

[DP]

between 1 - 30 kohms it will be the pcb

that is a very wide range of acceptable values of resistance,

A typical temperature sensing thermistor would be about 5 KΩ at 0°C and 2.9KΩ at 100°C

That said the one used in the boiler may be a very different type.

It would sensible to obtain a copy of the temperature / resistance graph for the type used in the boiler and use that to verify the thermistor is within the acceptable tolerance.

The thermistor circuit on the PCB could be tested using known resistors to replace the thermistor and thus simulate the thermistor being at various temperatures and verify that the control / indications are correct for those simulated temperatures.

5k at 0 degree seems very wrong. Wonder if the thermistor you have is also 500 years old and meter too, hence you are getting 5k at freezing point

Tony I read every post you make so I can learn something. What is a plud connector

 

[bernardgreen]

The thermistor I quoted temperature / resistance values for is the TDK B57891M0102+000 ( 1009 T/R curve )

Data sheet at

http://en.tdk.eu/inf/50/db/ntc_13/NTC_Leaded_disks_M891.pdf

The thermistors used in boiler temperature sensors are almost certainly going to be lower cost devices, most likely with a steeper T/R curve to simplify the electronics but at the cost of reduced accuracy in the temeperature measurement.