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fixer2013, Handyperson
Category: Home Improvement
Satisfied Customers: 82
Experience:  I am able to supply most answers for DIY projects, as I have many years experience
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Hi I have a Honeywell thermostat that runs heating and got

Customer Question

Hi I have a Honeywell thermostat that runs heating and got water and for the past 5 years I have been getting an F4 error code and the actuator makes a horrible noise as the pin notes backwards contemporaries...I can restart the system by turning the electricity off and on again and everything is fine for a while but then F4 appears again. I have had the actuator replaced twice so it can't be that surely...I am at a complete loss...can you help. I have a glow worm boiler
Submitted: 4 years ago.
Category: Home Improvement
Expert:  fixer2013 replied 4 years ago.

Hello I am sorry it has taken longer to get to you. I hope that I can help you today.


THe F4 code usually means a failure to ignite signal from the main PCB board. As you have replaced the actuator. Could you say that the water pressure in the system is low. less than 1.1 bar. If this is so the pressure switch will not operate from the signal ansd cause the ignition to operate. There is usually a small tap under the boiler, turn this to input more water into the boiler. If this does not solve the problem I would start to suspect the main board.

Please come back if you have checed this out and I will see if I can give you more tips.




Customer: replied 4 years ago.



I thought your advice had worked...however, even though the actuator no longer makes the horrendous noise it did before (like it was really struggling to move) which is likley dur to following your advice to turn up the pressure into the has started stating F4 on the thermostat control unit once again and switches off...which is only remedied by witholding the main power off and on again.


Do you suspect it could be the unit itself or perhaps the mother board by the boiler/tank? If so, who would be the best person to speak to..a plumber or an electrician? Thanks Darren

Expert:  fixer2013 replied 4 years ago.

Hello again Darren.


Oh dear, Im sorry that there is a faut again, I would now suspect the motherboard is not sending the ignition signal..


I would try and get a reputable heating engineer to test through the circuits for you.

I would not use an ordinary plumber or electrician.

I hope that they can get it sorted for you