Why would a relay be fitted to a heating system

[ElectriCall]

I have been asked to rectify a fault on a heating system, I have done lots of heating systems but never one with a relay. The heating engineer told me it was an s-plan, but it has a pump for the hot water as well as the heating and also has a "hot water off" wired to the timer.

The problem I have is that when the hot water is on and you switch the heating on, the hot water pump cuts out. The system used to work but recently failed. I'm assuming its the relay

Any ideas?

 

[monkeyelectric]

I have been asked to rectify a fault on a heating system, I have done lots of heating systems but never one with a relay. The heating engineer told me it was an s-plan, but it has a pump for the hot water as well as the heating and also has a "hot water off" wired to the timer.

The problem I have is that when the hot water is on and you switch the heating on, the hot water pump cuts out. The system used to work but recently failed. I'm assuming its the relay

Any ideas?

Have you tested anything? What is the relay connected to? Assume nothing!

 

[rmaynard]

It may be a relay for pump run-on?

Have a look here at the schematics - http://www.electriciansforums.net/central-heating-systems/25634-central-heating-schematics.html

 

[p11jor]

For window contacts maybe ? Seen them when window gets opened heating goes off

 

[monkeyelectric]

For window contacts maybe ? Seen them when window gets opened heating goes off

Thats for air conditioning surely?

 

[ElectriCall]

The relay is for the pumps, thats why I assume the relay is the fault, as the heating and hot water works individualy but not together

 

[monkeyelectric]

The relay is for the pumps, thats why I assume the relay is the fault, as the heating and hot water works individualy but not together

Have you tested any of it though? It may help if you draw the circuit out in front of you

 

[ElectriCall]

I've tested it and drawn it out, so I think I need to have a good look at it. The schemetics posted by "rmaynard" look usefull, thanks.

 

[R G]

I am thinking you have 2 pumps , 1 for heating and 1 for hot water wired into their own 2 port valves , is that right , and controlled by 2 channel programmer , you say their is also a hot water off return to the programmer , How is the relay bringing in the pumps , it could be that is the way it was planned , the relay was selecting either 1 pump or the other , with this in mind it could be that the heating zone is so large in relation to the boiler output that this is how it is, please supply more info if you can.....

 

[p11jor]

Thats for air conditioning surely?

It was on the heating systems on a student halls we did last year and again In the middle of one now too

 

[ElectriCall]

Yes, 2 pumps 1 for heating and 1 for water, wired to 2 valves, on valve has 5 wires the other has 4 (incl CPC) which is also confusing the issue. it is also a big house.

 

[adonis]

yes! just look the schematic read what the relay's function and learn also the sequence.

 

[R G]

Aha thats how it is the H W return answers the question . Thats the way it is designed mate....

 

[ElectriCall]

you say the heating zone might be large in relation to the boiler output, it has a huge boiler. If this is designed this way then would it be easy to make the water and heating come on together with the relay.

 

[R G]

Not sure , can you trace and draw it out then post it , it should be possible , just need to see a plan / drawing , you have 2 pumps here using the same boiler you see and if the boiler has return over run then it can only apply to 1 at a time , get a drawing done and we'll have a look mate.....