Feed from water pump straight back to boiler, with tap?

[cocjh1]

CH is working fine, but for interest wondered if someone could help explain the following please.

The pipe out my water pump (POST boiler output) splits three ways:
1) CH motorised valve
2) HW motorised valve
3) Pipe straight back to boiler input, with tap.

What is the need for the pipe back to the boiler? The tap is open, and can only think without it the water pump would get a bit upset when both valves closed and pump still running.

What stops all my newely heated water going straight back to the boiler, and circulating round the rads?

Ta,
Chris

 

[seco services]

What is the need for the pipe back to the boiler?
The tap is open, and can only think without it the water pump would get a bit upset when both valves closed and pump still running.

it's a bypass for when the hw/heating are satisfied and valves closed
but the pump is still running on pump overrun the water can still circulate.

What stops all my newely heated water going straight back to the boiler, and circulating round the rads?

Ta,
Chris

how will it circulate all the rads if both valves are closed ?

 

[cocjh1]

What stops all my newely heated water going straight back to the boiler, and circulating round the rads?

how will it circulate all the rads if both valves are closed ?

It won't. My question was worded badly.

When my valves are open, what stops my newly heated water going straight back to the boiler down this bypass pipe? Doesn't water behave like electricity and take path of least resistance?

Also, how open should the tap be please? fully, half, just open...

Thanks so far for the enlightenment

Ta,
Chris

 

[seco services]

open it about 1/4 to 1/2 a turn.
then it won't all bypass.

 

[D_Hailsham]

When my valves are open, what stops my newly heated water going straight back to the boiler down this bypass pipe? Doesn't water behave like electricity and take path of least resistance?

Correct, but not all the water will flow down the bypass, even if it is fully open.

how open should the tap be please?

That info should be in the boiler installation manual. However, the current solution is to fit an Automatic Bypass Valve (ABV). This is a spring-loaded valve which can be adjusted so that it only opens when the pressure in the circuit exceeds a certain value, i.e when a motorized valve closes or TRVs have closed down.

The typical setting for a manual valve is one turn open.

 

[cocjh1]

Thanks for the knowledge guys

My boiler is a Glow worm ultimate 70FF. From manual:

6.7 Adjustment - Fully Pumped Open Vented
and Sealed Water Systems
When commissioning the system the boiler should first be fired
with the bypass fully closed on full service, that is, central
heating and domestic hot water. Adjust the pump to the system
design setting then balance the system. Having achieved a
satisfactory condition operate the boiler with the bypass fully
closed on minimum load, normally this will be central heating
only with one radiator in the main living area operating. The
bypass valve should be gradually opened to achieve a
temperature difference no greater than 20oC between the flow
and return.
UNDER NO CIRCUMSTANCES SHOULD THIS VALVE BE
LEFT IN THE FULLY CLOSED POSITION.

How would you measure the temp difference between flow and return? Clamp on thermometers to the copper pipes sufficient?

 

[D_Hailsham]

How would you measure the temp difference between flow and return? Clamp on thermometers to the copper pipes sufficient?

Yes, or you can use an Infrared thermometer.

 

[tamz]

How would you measure the temp difference between flow and return

The flow will burn your hand and the return won't

Joke

Clamp on thermometers to the copper pipes sufficient?

Yes