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.....

 

[monkeyelectric]

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

How odd, i've not seen that for heating before only air con, what type of heating was it?

 

[ElectriCall]

Ah, so RayGalea, your saying that if there is a secondary return, which there is, a bronze pump, that it will only let one pump work in conjunction with the bronze pump?

 

[R G]

Yes , with the pump over run which is a pump feed back from the boiler , can only bring on 1 pump , because either heating or hot water valves are open

 

[ElectriCall]

So, the customer wants the heating and hot water at the same time, is there a way I can achieve this with the secondary return? they don't care what I have to do to acheive this

 

[R G]

You have 2 systems in effect , working from 1 boiler , I think that 1 off the pumps would have to be removed and flow from the boiler fed through just 1 pump then split to feed the 2x 2 port valves , so plumbing would need to be altered , also check to see if both2 port valves are spring return ,( usually are ) then wire the system as a S plan as normal .
So some plumbing is involved , Simply return it back to an S plan system ......

 

[R G]

Another thought , are the 2 pumps different sizes, it could be that the pump required for the heating circuit is too highly rated for the hot water circuit and has a smaller pump for the hot water

 

[HandySparks]

You have 2 systems in effect , working from 1 boiler , I think that 1 off the pumps would have to be removed and flow from the boiler fed through just 1 pump then split to feed the 2x 2 port valves , so plumbing would need to be altered , also check to see if both2 port valves are spring return ,( usually are ) then wire the system as a S plan as normal .
So some plumbing is involved , Simply return it back to an S plan system ......

I think you're barking up the wrong tree here mate. The clue is in the OP stating that the HW pump is a bronze one. These are typically used in conjunction with extra 'return' pipework to circulate the DHW around the house so that hot water is instantly available at each tap without having to draw off some cooler water first. It's nothing to do with the primary circulating water. I would expect this bronze pump to be on a timer, so that instant hot water is available whenever the users are likely to want it.

 

[R G]

Thats why I want to see some diagrams / drawing , It's difficult to picture without it......

 

[ElectriCall]

I'll draw it up later from my notes, the bronze pump is on a timer also

 

[Knobhead]

So you've worked lots of heating systems? Not come across a relay? Don't take on work you're not competent to do.

 

[mark ju]

Regarding relays on heating systems...
One of the original types of mid position valve used to have a separate relay, forget the make.
Also few years back I did a heating system which consisted of three different zones plus hot water etc and various pumps and that required the addition of several relays. It were A reet bugger. Spent a while working it all out, finished it off and on packing up found the schematic for the system in the back of the boiler manual !
So might pay to start by having a look at any info the householder might have, boiler manuals etc.

 

[Deleted member 9648]

Some boilers have a no-volt trigger......in which case a relay may be needed.

 

[markythesparky]

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.

could we see?

 

[rmaynard]

could we see?

The links are in my post on the first page