40cdi internal thermostat replacement

[finlaand]

Hi there

This a job I need gas engineer for?

It's a 40cdi system boiler, 10 years old, all works fine but last two weeks started firing on for a few mins, hits 60c usual temp, then stops, and repeats this maybe every 45mins of the day.

Pump fine and all works when meant to work bar this... I have switched off hot water and heating on the controls,set to away mode and even then above still happens. Hence assume it's internal thermostat.

 

[CBW]

Don’t assume anything! It sounds more likely to be a motorised valve failure.

 

[Madrab]

+1 -

that wouldn't usually be the internal HL stat that would cause that. Something is telling the boiler to fire up - what does that would be the areas I would rule out first.

 

[finlaand]

Ok, well I did first notice all this as one rad upstairs was like warm, then saw boiler on in first place...I had already replaced that motorised value, but maybe the timescale stuff I have not scraped enough off and it's sticking so no closing fully..
Ok I'll check that didn't think that would cause the boiler to do anything if controls are all set to holiday mode for last four days

 

[CBW]

didn't think that would cause the boiler to do anything if controls are all set to holiday mode for last four days

It will override controls as there’s a permanent live and if it makes with the switch live then the boiler will activate.

 

[Madrab]

presume it is a 2 port valve?

As suggested - they carry a perm live, when the programmer calls for heat it sends power to the actuator motor, the motor opens the valve and then the lever closes an internal microswitch that sends the permanent power to the boiler, turning it on. Only thing with that though is the boiler would stay on all the time (pump), firing up every now and again once the temp dropped enough.

If that's what's happening then time to check out the actuator (2 port)

 

[finlaand]

Ok narrowed it down...I replaced as said a few weeks back the motorised value, danfoss hpa2, but not the bit behind you also get in the pack, metal bracket on the pipe...

I removed the motorised value, it's closed, so all good, but metal bracket is in closed position but heat gets though, must have failed...

Just need to work out how to change without draining whole system down

 

[DP]

Is that boiler heating the whole street? 40kW
What size of house do you have

 

[finlaand]

ha Actually solid wall 1780's place with 33-36cm thick walls outside, no insulation on them, and 17 rads and lots of heat loss, so kindof just about copes mid winter.. been slowly pulling back internal walls to add in 50mm insulation, so hopefully yes in a year or so when its time to replace this 16 year old boiler, ill go for less power..