Pipe thermostat placement/back boiler flow.

Yuppie

Hi guys.

Moved into a house recently enough and it has an 18" grant back boiler in the fireplace. pump was knackered so replaced that and everything was working fine. The pump was activated by a manual switch (in this case plugging it in).

Fitted a pipe thermostat to the outflow pipe from the back boiler as close as possible to the boiler ( i think its well within a meter). Electrical circuit is correct as the pump triggers when you turn the dial down far enough.

Have been trying to dial it in over the past few nights with no luck. tonight had a full fire i.e. full width of the grate, good flame lots of coal etc, for a full hour but the pump wont trigger unless i turn down the dial to nearly room temp then back up to the usual 45/55.

Went up stairs to check the tank and the pipe going into it was warm/hot.

when the water heats from the fire should a certain amount not flow naturally out towards the stat and trigger it to turn the pump on?

Or am i missing something obvious?

Dtp1979

Yuppie wrote: »

Hi guys.

Moved into a house recently enough and it has an 18" grant back boiler in the fireplace. pump was knackered so replaced that and everything was working fine. The pump was activated by a manual switch (in this case plugging it in).

Fitted a pipe thermostat to the outflow pipe from the back boiler as close as possible to the boiler ( i think its well within a meter). Electrical circuit is correct as the pump triggers when you turn the dial down far enough.

Have been trying to dial it in over the past few nights with no luck. tonight had a full fire i.e. full width of the grate, good flame lots of coal etc, for a full hour but the pump wont trigger unless i turn down the dial to nearly room temp then back up to the usual 45/55.

Went up stairs to check the tank and the pipe going into it was warm/hot.

when the water heats from the fire should a certain amount not flow naturally out towards the stat and trigger it to turn the pump on?

Or am i missing something obvious?

How close to the boiler is the stat? Is there a gravity circuit on the back boiler?

Yuppie

Dtp1979 wrote: »

How close to the boiler is the stat? Is there a gravity circuit on the back boiler?

The pipes are within concrete at the right hand side of the fireplace but i'm fairly sure its within 1m of pipework from the boiler. its as close as i can get it in a confined space.

There is pipes on the left hand side of the fireplace (behind coverings) that seem to be the gravity circuit. i.e. when the fire is going i can go upstairs to hot water tank and there is a flow of heated water to it(with no pumps running).

Dtp1979

Yuppie wrote: »

The pipes are within concrete at the right hand side of the fireplace but i'm fairly sure its within 1m of pipework from the boiler. its as close as i can get it in a confined space.

There is pipes on the left hand side of the fireplace (behind coverings) that seem to be the gravity circuit. i.e. when the fire is going i can go upstairs to hot water tank and there is a flow of heated water to it(with no pumps running).

1 m from the boiler is perfectly fine. Turn your stay to 70. Of the cylinder water gets really hot and no pipes are banging or gurgling then you probably have a gravity circuit.

Dtp1979

Dtp1979 wrote: »

1 m from the boiler is perfectly fine. Turn your stay to 70. Of the cylinder water gets really hot and no pipes are banging or gurgling then you probably have a gravity circuit.

The fact your stay isn't kicking in might indicate a faulty stat maybe. Is it secured tightly to the pipe?

Pete67

Sounds like the OP has a 4 pipe system with the gravity circuit on the left hand side of the boiler, and a pumped circuit on the right hand side. There may not be enough (or any) gravity flow through the pumped circuit to heat the pipe stat to a reasonable temperature. If it can be done easily, move the pipe stat over to the gravity circuit and set it at 70C. This will bring on the pump once the hot water cylinder is heated.

K.Flyer

Yuppie wrote: »

[...]
Fitted a pipe thermostat to the outflow pipe from the back boiler as close as possible to the boiler ( i think its well within a meter). Electrical circuit is correct as the pump triggers when you turn the dial down far enough.

Have been trying to dial it in over the past few nights with no luck. tonight had a full fire i.e. full width of the grate, good flame lots of coal etc, for a full hour but the pump wont trigger unless i turn down the dial to nearly room temp then back up to the usual 45/55. [...]

Does your pipe stat have 3 wiring terminals.. from your description you may be connected the wrong way.
Try swapping the cable going back to the pump to the other terminal, eg if C is live and the switched cable is on terminal 1, change it to 2. If thats not your problem, then as DTP says, probably a faulty stat.

Yuppie

Access to the gravity circuit side isn't easy without ripping off covered sections around the chimney breast. The Stat is fine in my opinion as it triggers when you turn the dial down to room temp and turns off when you turn it back up. tested it with a hot water bottle before i put it on as well. Attached it to the pipe firmly with the little wire spring that came with it and a bit of ECU thermal compound.

Id agree there seems to be 2 circuits. Left side gravity fed to the tank, right side pump circuit to the rads.

going back to the stat, it works, the pipe that it is mounted on is cool to the touch even when the fire is going. if i manually activate the pump via the stat the pipe warms immediately and i could readjust the stat to the correct setting. Defeats the point of putting the stat in in the first place really.

Anyway assuming there is those two circuits. when the fire is going should water not moved out through all the exits it can due to normal thermal expansion etc? or is there enough resistance in the pumped circuit that it will never flow enough water out to trigger the stat?

Pete67

Yuppie wrote: »

Anyway assuming there is those two circuits. when the fire is going should water not moved out through all the exits it can due to normal thermal expansion etc? or is there enough resistance in the pumped circuit that it will never flow enough water out to trigger the stat?

Sounds like there is no flow through the pumped circuit until the pump is running. Can you move the pipe stat up to the hot press to get access to the gravity circuit? It would work fine there too.

Yuppie

Pete67 wrote: »

Sounds like there is no flow through the pumped circuit until the pump is running. Can you move the pipe stat up to the hot press to get access to the gravity circuit? It would work fine there too.

That'd be one really really long wire to run all the way back down to the pump :rolleyes:

if the pumped side is a getting no flow at all i may have to take a hammer and saw to the coverings on the gravity circuit on the side of the chimney breast.

Blunt force interior decorating:P

Dtp1979

Yuppie wrote: »

That'd be one really really long wire to run all the way back down to the pump :rolleyes:

if the pumped side is a getting no flow at all i may have to take a hammer and saw to the coverings on the gravity circuit on the side of the chimney breast.

Blunt force interior decorating:P

The stat will read most accurately if on the gravity side, and not the pumped side. How far away is the cylinder from the boiler?

Yuppie

Dtp1979 wrote: »

The stat will read most accurately if on the gravity side, and not the pumped side. How far away is the cylinder from the boiler?

The tank is a good 16m or so form the boiler. on the first floor.

Dtp1979

Yuppie wrote: »

The tank is a good 16m or so form the boiler. on the first floor.

That's way too far

Yuppie

Hi

digging up a dead thread i know, but last week i cut a little hatch in wood panel covering the gravity circuit and moved the thermostat to that pipe and traced the wiring back round to the pump on the other side.

Problem solved, pump triggers perfectly now with the stat set to 65C.
Thanks for the help!