Combi Boiler where are the sensors

[steph57]

Hello folks,
Sorry for this rather basic ignoramus question but anyway here goes. We have a Worcester oil fired combi bolier and recently did up our utility/boiler room and installed a sink, which was plumbed in by our excellent local plumber. What we are finding is that operating the hot tap on this sink does not always seem to fire up the boiler, even when the boiler is all switched on and geared up for action. However, as soon as we operate the hot tap in the kitchen or bathroom the boiler fires up as normal and we then get copious hot water through the new sink in the utility room.
Although the new sink is close to the boiler, the hot water feed to the washing machine and the new sink comes down from somewhere under the upstairs floor.
All of which has set us wondering, where does a combi boiler pick up information on flow/temperature/pressure in order to switch on the boiler when needed? We had assumed that all of this was within the boiler itself but maybe there are sensors in the system somewhere, hidden under the upstairs floor and which are being missed by the feed to this new sink?
Not a huge problem, all we have to do is run the hot water tap in the kitchen or bathroom and the boiler fires up and provides hot water to our new utility sink but it is a bit of a puzzle, any thoughts on this? We would have gone back to our plumber but he is stacked up with so much work we did not feel wed should trouble him.
Thanks

 

[Burnerman]

Do you get a good flow out of that hot tap, Steph - or maybe it's just a trickle due to restrictions in the tap connectors or whatever?
Can I ask which particular boiler you have?
John

 

[endecotp]

where does a combi boiler pick up information on flow/temperature/pressure in order to switch on the boiler when needed? We had assumed that all of this was within the boiler itself but maybe there are sensors in the system somewhere, hidden under the upstairs floor and which are being missed by the feed to this new sink?

You are correct, the sensor is a pressure sensor inside the boiler. At least, it is in every system I've ever known about.
Do you get hot water - eventually - from other taps if they are just partially open? Or does the boiler only start when the taps have a high flow rate?
Is your incoming cold water pressure reasonably high?

 

[Agile]

Actually, it is not a pressure sensor!

It is a flow sensor, often in the form of a turbine in modern boilers.

Older boilers tended to use a magnetic shuttle operating a Hall effect sensor.

Tony

 

[Steelmasons]

Older boilers tended to use a magnetic shuttle operating a Hall effect sensor.

Tony

I think you'll find a water section was used that incorporated a diaphragm coupled with a micro switch..

 

[Terrywookfit]

Actually, it is not a pressure sensor!

It is a flow sensor, often in the form of a turbine in modern boilers.

Older boilers tended to use a magnetic shuttle operating a Hall effect sensor.

Tony

Actually it is a simple flow switch that operates a relay !!!

 

[muggles]

Actually, it is not a pressure sensor!

It is a flow sensor, often in the form of a turbine in modern boilers.

Older boilers tended to use a magnetic shuttle operating a Hall effect sensor.

Tony

I've never seen a turbine in an oil boiler Tony...

 

[steph57]

Hello folks,
Thank you for your comments, it sounds from what you say that all the sensors, whatever they are, that turn on a combi-boiler are within the boiler itself? We have 4 hot water taps coming off our combi-boiler (Worcester Greenstar Heatslave 18/25) fed hot water system, 3 of these taps, when operated, will cause the boiler to fire up however, the hot tap in out new utility sink does not seem to want to trigger the boiler to fire up. Once the boiler is fired up all our hot water taps, including the new one, will deliver copious amounts of hot water at a good pressure.
Hence we wondered if the supply to the new sink was somehow by-passing some sort of sensor but it sounds as though this is unlikely to be the case?
This is not an insurmountable problem but it does seem to be a bit of a puzzle, thank you for your thoughts on this.

 

[bernardgreen]

Actually it is a simple flow switch that operates a relay !!!

OK but what is the mechanism that switches the supply to the relay coil ?

 

[Agile]

Your boiler responds solely to a hot water flow.

They normally need a minimum flow rate of 2.5 litres per minute. You can easily measure that. See the FAQ if you need help.

There may be a problem called a crossover at your new tap.

To test that you would need to turn off the water supply going in to your boiler. When you have done that you should get no flow at all from any hot tap.

Tony

 

[DP]

Shuttle in flow sensor sometimes operates a simple reed switch

 

[bernardgreen]

and in some types of boiler a turbine produces electrical impulses that are "counted" to determine how much water is flowing. Maybe this affects the modulation setting of the burner, or maybe not.

 

[AGAS]

and in some types of boiler a turbine produces electrical impulses that are "counted" to determine how much water is flowing. Maybe this affects the modulation setting of the burner, or maybe not.

this is how you measure the flow rate through DC on the PCB board

 

[ianmcd]

newer taps come with 10mm flexi hoses as the connection and it might be that the new basin is not getting enough of a flow rate to tell the boiler to fire , your other taps are fine so there is no problem with the boiler the problem is in your basin install

 

[Terrywookfit]

and in some types of boiler a turbine produces electrical impulses that are "counted" to determine how much water is flowing. Maybe this affects the modulation setting of the burner, or maybe not.

The boiler is a Worcester OIL FIRED combi. All models use a FLOW SWITCH to activate relay 4 !!!


The domestic mains water inlet is connected to a flow switch which detects when a domestic hot water tap has been opened.

This activates the burner and pump via relay.