Heating control question with an oddity

[CountryFan]

I’ve not done many heating controls and wanted to know, on a standard 2 zone heating system with a combi, existing programmer is rated as 6 and 2.5A (resistive and conductive I think) can I swap to a lower rated 3A one? Since, surely the fcu fuse will only be rated at 3A anyway.

Also, the oddity, but me (gas engineer) and the electrician think it’s coincidence: The customer was complaining that when she put her heating on it works fine, but once the temperature drops and the thermostat kicks in again, the smoke alarms go off. I’ve been and checked the wiring, which seems ok, couldn’t see any shorts and the download from the heat/CO in the kitchen (where the boiler is) doesn’t show any CO. Nothing is penetrating the wiring, eg a nail in the wiring. No gas cooker and she claims it does this every time. I’ve swapped the alarms - previously the optical alarm with 9v battery backup to multi sensor fire alarms. Anyone else had something similar? It worked fine when I was there.

 

[Harry Bloomfield]

I’ve not done many heating controls and wanted to know, on a standard 2 zone heating system with a combi, existing programmer is rated as 6 and 2.5A (resistive and conductive I think) can I swap to a lower rated 3A one? Since, surely the fcu fuse will only be rated at 3A anyway.

More likely 6amp resistive load, 2.5amp inductive! An inductive load, is higher when switched both on, and off. Such that it can weld contacts up due to the current surge, and spark. A resistive load is much gentler on contacts. Your 3amp fuse, will not care so much whether the load is inductive or resistive, because it has some inertia - it takes it some time to respond to an overload.

 

[CountryFan]

More likely 6amp resistive load, 2.5amp inductive! An inductive load, is higher when switched both on, and off. Such that it can weld contacts up due to the current surge, and spark. A resistive load is much gentler on contacts. Your 3amp fuse, will not care so much whether the load is inductive or resistive, because it has some inertia - it takes it some time to respond to an overload.

Sorry, still don’t understand what that means. I understand I’ve got the 2 the wrong way around. There is some brown thermal damage on the front of the existing programmer/timer.

 

[Harry Bloomfield]

The customer was complaining that when she put her heating on it works fine, but once the temperature drops and the thermostat kicks in again, the smoke alarms go off.

They are responding to the inductive pulse spark, across the contacts. You can fit suppressors across the contacts, which might help.

There was a certain pump, and boiler combination, where the pump was switched by the boiler. The switching was so inductive, that it would weld up the relay contacts in the boiler, needing the pcb to be replaced. The boiler manufacturer, sold a suppressor to deal with it.

 

[CountryFan]

They are responding to the inductive pulse spark, across the contacts. You can fit suppressors across the contacts, which might help.

Since there is already some thermal damage, and it makes a grinding noise apparently, can I change the programmer for a digital 2 zone one, rated as 3[1]?

I think the boiler/pump you’re referring to is a Worcester?

 

[Harry Bloomfield]

There is some brown thermal damage on the front of the existing programmer/timer.

That could be due to many things.

Since there is already some thermal damage, and it makes a grinding noise apparently, can I change the programmer for a digital 2 zone one, rated as 3[1]?

Grinding noise suggests it is a mechanical unit? A digital 2 zone ought to be designed to cope with the expected load type, so why not, especially, if the boiler is switching the pump on? The only load on the digital programmer, will only be carrying the current for the valve, and the signal current for the boiler.

 

[CountryFan]

Grinding noise suggests it is a mechanical unit?

Yes, it is.

if the boiler is switching the pump on?

Yep, it’s a combi boiler. 2 zone setup

 

[Harry Bloomfield]

Yes, it is.

Yep, it’s a combi boiler. 2 zone setup

I would put the brown discolouration down to the motor over-heating, due to age, wear and tear.

 

[CountryFan]

I would put the brown discolouration down to the motor over-heating, due to age, wear and tear.

I definitely thought overheating, as it was warm today when she had the heating on and not near another heat source. I’ve already put it down to be replaced, so it’ll either be a gas engineer or electrician. Thanks Harry.

 

[CountryFan]

Still happening since me changing the alarms. Going tomorrow to change the programmer and get an electrician too.

 

[ericmark]

I will have a guess, that the two devices both use the same frequency for some form of wireless coms, and there are interfering with each other.

Years ago it was a big problem, but today EMC filters are normally of a better quality to stop it.

Years ago, I had to walk the dog, and I would chat on the local repeater GB3MP while doing so, the amount of security lights I trigger had to be seen to be believed. As to driving down an empty street but for one vicar and all the car alarms going off, he must have thought it was an act of god!

As to an electrician even knowing what a wave meter is, never mind having one and being able to use it, not so sure, I do have one, and have passed my RAE plus have Fdeng behind my name, and I would not really know where to start. There are other radio hams on this forum, maybe they do?

I had a problem with a thermostat in late mothers' house, and only cure was to replace it.

 

[CountryFan]

I will have a guess, that the two devices both use the same frequency for some form of wireless coms, and there are interfering with each other.

Everything is hard wired, even the inter connect on the alarms. It also works fine when heating initially is on, only when the temperature drops and it kicks back in so they sound.

 

[ericmark]

My Nest Gen 3 is hard-wired, but it still uses radio signals. Be it radio, or simply two cables too close together, it looks like an EMC problem.

 

[CountryFan]

My Nest Gen 3 is hard-wired, but it still uses radio signals. Be it radio, or simply two cables too close together, it looks like an EMC problem.

Surely that would set it off all the time, or if I operate the thermostat? This is just when it cools down and kicks in. Mechanical programmer, mechanical thermostats.

 

[Harry Bloomfield]

I will have a guess, that the two devices both use the same frequency for some form of wireless coms, and there are interfering with each other.

It a steam powered mechanical timer!