Pipe Thermostat Blown

[F1yTrap]

Hi,

For the past couple of weeks I have noticed that the central heating seems to be running too hot. there is also a bubbling sound coming from the pipework around the hot water tank.

I assumed this to be a because of a failing stat. I have a pipe stat in my living room (Honeywell L641A1013), which I tried turning down half way. This didnt cure the problem so I turned it down as far as it would go. As I did this there was a big flash and a loud pop from the insite of the stat!

This caused the swich fuse to the boiler to blow. I assume I need to replace the pipe stat, but could this be a symptom of another problem? What would cause such a flash and pop?

Cheers,
Craig

 

[D_Hailsham]

Sounds a strange set up You don't normally find pipe thermostats in the living room.

What is its purpose?
Which make/model boiler do you have?
What other controls do you have for heating and hot water?

 

[F1yTrap]

"Sounds a strange set up" - your not wrong. I think the whole system was fitted by cowboys before we moved in.

Its an oil system with the boiler outside. In the living room I have a pipe sensor (the one that blew) and the main controller (one of the old dial sort).

The boiler is outside in a small brick room build onto the chimney. In the "boiler room" I have a Worcester - Danesmore oil boiler. There is a temperature stat to detect low temps/frost (and turns on the boiler) and another pipe stat, set to 60, on a 22mm pipe coming out at the top of the boiler.

Since my first post I dismantled the pipe stat in the living room, I could see that one of the soldered joints had broke, which is what would have caused the flash. I have resoldered an re-installed the stat.

I replaced the blown switched 5A fuse which supplies the boiler and switched on.

The system started fine, to I decided to test the repaired stat. With a screwdriver I turned down the stat until the click. The system turned off and I though it was fixed, however, when I turned up the stat again it didn't come back on. I discovered that the main 5A fuse had blown again.

Any ideas why a stat would cause the main fuse to blow?

 

[D_Hailsham]

In the living room I have a pipe sensor (the one that blew)

What temperature is this normally set at?

I can understand the need for a frost stat in the boiler house,but a second stat set to 60 is unusual. Presumably the boiler has it's own thermostat.

How is hot water temperature controlled?

Any ideas why a stat would cause the main fuse to blow?

The obvious answer is: something shorting. I would need a wiring diagram to give a more helpful answer.

Which Danesmoor do you have?

 

[F1yTrap]

The boiler is a Danesmoor Utility (not sure which one, probably 12/14).

The Stat on the boiler is set to 1, the pope stat in the boiler room is set to 60. The pipe stat in the living room is (and always has been) set to about 80.

I have never had any need to alter any of the stats, its always been fine until there recent overheating.

Im wondering if the livingroom stat has always been problematic, hence why it was set so high. Since my last post, I have replaced the fuse (again) and kicked up the system (hot water only), I adjusted the boiler room pipe stat and it shut off the stystem as expected, and restarted it when I restored it to the correct position. Tried the same thing again on the living room but it popped the fuse again.

I have replaced the fuse and st the living room stat to high. When the water starts bubbling again I will try and control it with either the boilers stat, or the pipe stat in the boiler room.

One thing I have been wondering, its quite cold outside and I think that the low temp stat is currently on. Could it be that the stats are wired up incorrectly and that when the outside stat is ON and when the inside stat switches, that it causes a direct short??? If so this could have been a historical issue, and some other cowboys fitted an extra pipe stat rather than fix the problem?

 

[londonboy]

So you have two pipe stats? What does each one do? What pipe are they on?

 

[D_Hailsham]

The Stat on the boiler is set to 1, the pope stat in the boiler room is set to 60. The pipe stat in the living room is (and always has been) set to about 80.

A setting of 1 for the boiler stat is a temperature of about 55°C - which is very low. It would normally be about 75°C.

I can't see why the pipe stat in the boiler room should be set to 60°C. It is normal to have a pipe stat in conjunction with a frost stat, but set to a temperature of about 20°C. The idea is that the frost stat turns the boiler on if it gets too cold and the pipe stat turns it off when it had warmed up - but not too much.

As for the living room sat - that's a mystery.

A wiring diagram is definitely needed.

I am wondering if the boiler's own thermostat is faulty and the other pipe stats are a workaround?

 

[londonboy]

Im wondering if its for a pump overrun?

 

[electronicsuk]

Perhaps the original installer has cocked up and wired a neutral into the wrong terminal, such that when the heating demand is satisfied, live is being linked directly to neutral. I cannot see any other way that a fault with the stat would be allowing enough current through to blow a 5A fuse. Unless, of course, there is a fault with whatever the stat is supposed to be switching.

 

[D_Hailsham]

WIRING DIAGRAM

 

[F1yTrap]

Thank you all for your input.

I have run out of 5A fuses for the time being, I have the heating on now so that will do me for tonight.

When I get some more fuses I will try setting off the thermostats together, I think that you might me on to something 'electronicsuk', I suspect there could be some incorrect wiring at play.

Im not so sure the pump is at fault as the pipe stat in the boiler room manages to successfully shut down and restart the system (I think). The pump is located under the floorboards and is a real pig to get to, so while I have heat Im going to leave things be. (That is until it gives up the ghost at around 6pm Christmas eve!).

I will post back if I manage to unearth the problem.

Thanks again for all your input.

Craig