I am currently a bit baffled.

Over the last day or so, my central heating boiler seems to have been "firing up" a bit more often than normal (especially considering that the outside temperature has been "mild" for the last couple of days.

I turned my room thermostat down, and there was a "click" as it went past the actual temperature - so i assumed that my boiler would turn off (heat only setting, no hot water). However it didn't :confused:

I tried the controller itself, but even turning off both CH and hot water, the boiler continued to fire.

Thus, even with the thermostat saying "don't turn on", and the controller saying "everything off" - my boiler continues to work.

So i checked my pump. For some reason, even with the thermostat and controller saying NO, it keeps on spinning. However, if i switch it to slow speed it (seems to) turns off (for a while), but then continues circulating after a short time.

Thus i am baffled. I always thought that the room thermostat triggered the pump, so that implies that either the thermostat or the pump is faulty (hence pump almost always on). However, the controller failed to turn off the system (CH or hot water), and i can't believe that two independent components have broken at the same time.

So, does anyone have any ideas what might be going on (and any tests to confirm it)??

Background info is that it is a 20-year-old open system balanced-flue boiler, honeywell room thermostat, grundfos pump and ACL controller.

Thanks in advance,

mb

Duff Frost stat?

Could have kicked in over the cold spell and stuck on?

ALi-B,

a Duff Frost stat sounds surprisingly like the cause - except that as far as i know, i don't have one :confused:

I haven't found a separate sensor, and my boiler is in the kitchen - thus would be nowhere near the trigger temperature.

However, the fact that turning both the thermostat and the heating controller off doesn't stop the pump, suggests that such a device could be the problem.

The good news is that after turning the boiler off for a day (Monday), everything seems to be back to normal again - so fingers crossed, it was a freak occurence! However, if anyone else has any ideas as to what could have cause the problem - i am all ears!! Do (old) boilers have secret frost stats?

Oh, and sorry, i would have reported back last night, but the new-style ScoobyNet had confused my profile ;) Sorted now though :)

Cheers,

mb

There should be a 'frost stat' IN the boiler, so even though you don't know that you have one, you almost certainly have, they fit them as a safe gaurd against the boiler freezing!

There should be a 'frost stat' IN the boiler, so even though you don't know that you have one, you almost certainly have, they fit them as a safe gaurd against the boiler freezing!

I've never seen a frost stat built into a 20 year old balanced flued boiler.

Mog

yep as Mog.....it could be anywhere!! depends on how imaginative the plumber that fitted 20 years ago was! :D

By all rights it should have one...sometimes they are fiited in the coldest part of the house that has water pipes, sometimes it's just by the boiler.

The only suggestion as to finding it (if there is one! ;) ) is to trace the wiring from the boiler and control unit.

I know that some boilers (including some quite ancient designs) have a signal feed-back loop whereby the pump recieves a signal from the boiler/controller to tell it to continue running after the boiler has shut down the main burner. As I understand it, this is a designed-in safety feature. It's designed to reduce any heat build-up in/around the heat exchanger to safe levels by continuing to distribute any latent heat around the house for a short period after the main burner has swtiched off.

Hope this makes sense.

I know that some boilers (including some quite ancient designs) have a signal feed-back loop whereby the pump recieves a signal from the boiler/controller to tell it to continue running after the boiler has shut down the main burner. As I understand it, this is a designed-in safety feature. It's designed to reduce any heat build-up in/around the heat exchanger to safe levels by continuing to distribute any latent heat around the house for a short period after the main burner has swtiched off.

Hope this makes sense.

what you are describing is the pump over-run but that doesn't have the capability to fire up the boiler.

Mog