Circulation pump stat

billy_beckham

Hi Folks,

Quick sanity check, circulation pump on oil boiler should turn on only when stat hits setpoint. Boiler fires up, heats water, stat sees heat and turns on pump.

Correct?

John.G

No. Boiler and pump both start up when the roomstat or if manuallly switched, the boiler will continue to fire until its own thermoswitch is satisfied and the burner cuts out but the circ pump will/should continue to run until the roomstat or programmer or manual switch tell the boiler+circ pump to stop. In short once there is a demand for heat the oil boiler (burner) will cycle on/ff continuously but the circ pump will run continuously.

billy_beckham

Hi,

There is no room stat, the stat I'm talking about is on pipe coming out of the boiler. The boiler is on on a timer, separate electrical supply to stat and circulation pump.

Does that change things?

billy_beckham

Found this, think I am correct?

jimf

correct if you have a backboiler as in a solid fuel source

incorrect if you have an oil boiler

billy_beckham

OK, but the way the current setup is I struggle to see how it should work other than the way a back boiler is done.

The oil boiler is controlled by a timer.

A separate electrical supply goes to the stat/pump.

What difference does it make whether its oil or back boiler?

Wearb

I've come across a few done like that. It works as a crude pump over-run. Needs to be close to the boiler if outlet drops down as it will then depend somewhat on conduction as well as convection to to kick it off.

jimf

if the pump continues to run for too long after the timer goes off it will continue to cool the water in the rads

some boilers can suffer nuisance trips if the boiler and the pump go off at the same time as wearb says above a lot of these trips can be because of the set up of the pipework from the boiler or from the run stat been set too high

Wearb

"if the pump continues to run for too long after the timer goes off it will continue to cool the water in the rads"

Yes, and an even bigger problem can be the way it cools the cylinder. Good stat temperature setting and positioning is probably important. It is a crude way of doing it.

jimf

exactly people often wonder why their hot water is not lasting

billy_beckham

"if the pump continues to run for too long after the timer goes off it will continue to cool the water in the rads"

Yes, and an even bigger problem can be the way it cools the cylinder.

If the stat is set for say 60 degrees surely that would not allow either rads or cylinder to cool too much?

Pipe stat and pump are within 18 inches of the boiler.

Wearb

The problem is that it needs to be low enough to cut in before the boiler cuts out on the boiler stat. At this point in startup, the temperature of the boiler outlet pipe will vary a lot with distance from the boiler, especially if pipe drops immediately from the boiler.

If its working OK, then it's most likely that it has been set up as well as possible.

monseiur

https://www.boards.ie/discussion/2058278744/circulation-pump-stat

A neighbour of mine has a similar system to yours, house was built in early 1950's and central heating was retro fitted early 1980's (I think!) It's an indoor boiler fitted within 5 feet of the cylinder. The stat is on pipe between boiler and cylinder and has it's own separate power supply, the stat operates the circulating pump. The boiler itself has a built in time clock. The heating system is not zoned, so the whole house is heated including the cylinder every time the boiler kicks in. The hot water from boiler is pumped thru coil in cylinder on it's way to rads. House has a solid fuel stove which also heats water in cylinder directly (as in direct cylinder system) so to stop the cylinder from constantly boiling over the stove fire is let out once CH kicks in in the evening. A rather interesting set up.

jimf

must have no non return valves fitted