Log Burner Working Along Side An Oil Boiler

Customer asked me to wire up heating system with

Oil boiler

3 Port Motorised valve

Stat on Water Tank

No stat on Central heating

Then to wire in control to automaticaly bring in pump when log burner is lit

So oil boiler wired up to three port valve in usual way all works fine

So how to get log burner to operate Pump

I am thinking if I put a pipestat on Flow pipe from log burner to control pump

If I wire the pipestat as follows I think it will do the Job

N/C terminal to the pump output from the boiler

N/O terminal to the permanant live

COM terminal to the Pump

So in operation if oil boiler is turned on pump is operated via N/C terminal

Pipework heats Up and Pipestat switches from N/C to Normaly open feeding pump with 230v

Boiler turns off and Mid position valve returns to middle position but pump carries on running until pipework has cooled down enough for the pipestat to return to its normally off position. (bit like a pump overrun)

If Log burner is lit heat in flow pipe operates pipestat and pump is switched on.

This is how I think it needs to be wired. Any comments from anybody who has done this type of system before of has knowledge of the correct way

Hope my explanaton makes sence and thankyou for any helpful coments.

Rick

More questions than answers I am afraid, it's a very complex system.

The crucial thing is how is it all plumbed? New build or has the log burner just been tacked on to an existing system? What sort of tank, conventional or heat store? or just a neutraliser to combine to two heat sources?

Is the central heating drawing water from the tank, or are you trying to heat the radiators in real time from the stove? (very poor solution)

How does the heat get from the log burner to the tank? It will need large diameter, short, vertical pipe runs to flow entirely by gravity, so is there a second circulating pump for the log burner?

Firstly a pipe stat on the flow from the log burner is a very poor solution.  Yes it will turn on when you light the stove, but in all probability it might keep running after the stove has gone out, particularly if the stove flow is pumped.  A better solution is a stat on the flue to detect when the stove is actually light.

It's no good just turning the pump on in isolation, you need to operate the motorised valve as well. so the thermostat needs to simulate a heating demand to bring the 3 port valve into heating position and then turn the pump on. So you will need to do a bit of sketching out of the wiring and probably connect the stat across the heating contact on the timeswitch.

It's probably too late , but for anyone thinking of designing such a system from scratch, here's the best solution I have yet found:

Heat store tank, so you can have as many heat sources as you like.

boiler heats the tank only stopping when the tank reaches a pre set tank temperature.

CH controlled by timer and room stat takes heat out of the tank. via pump and 2 port valve.

HW available any time tank is hot and at mains pressure too.

Flue stat on stove to turn on circulating pump if needed.

Second "over heat" stat on heat store tank to override timer and room stat and dump heat to heating if the tank starts getting a bit hot.

Hi Dave

thanks for the reply and realise I have a bit of work to do yet in getting the final system working in an ideal manner but first off I need to make it safe then I can add to the controll aspect. The system is piped to a conventional Large indirect cylinder and yes it has a 28mm dia pipe running up to it. this system was piped up a couple of years ago and the plummer has long since gone. The oil boiler and valve has never been wired up before apart from boiler on a plug and run and tested. The customer has always just plugged the pump into a wall socket when the log burner was in use. I am trying to work out a safe method of using the two units. I had thought that attachingg the pipestat to the log burner would be better but had not thought about putting it on the Flue. I will have a bit of a work out over the weekend but just wanted to get some initial thoughts from people with experiance.

Rick

ProDave said:

More questions than answers I am afraid, it's a very complex system.

It's probably too late , but for anyone thinking of designing such a system from scratch, here's the best solution I have yet found:

Heat store tank, so you can have as many heat sources as you like.

boiler heats the tank only stopping when the tank reaches a pre set tank temperature.

CH controlled by timer and room stat takes heat out of the tank. via pump and 2 port valve.

HW available any time tank is hot and at mains pressure too.

Flue stat on stove to turn on circulating pump if needed.

Second "over heat" stat on heat store tank to override timer and room stat and dump heat to heating if the tank starts getting a bit hot.

Click to expand...

Agree with P-Dave...

I would be looking at getting the 3-port valve out of the system

and use multiple 2-port valves where needed to give greater control over what you heat where and when.

With these sort of systems you have to first think.. HOW DO YOU WANT THE SYSTEM TO WORK....

Then you can start to think about how to wire it!!

Consider some scenarios..

Customer may want Hot water and/or Central heating and/or Towel rads operating..

Maybe simultaneously or maybe individually?

Sometimes the weather is warm.. so log burner not in use...

Other times the weather is cooler and the Log burner is going...

Sometimes the log burner is only going late in the evening

but they may still want hot water & towel rads early evening or the following morning...

This type of logic only leaves one sensible conclusion as P-Dave says...

A common heat store that can supply all of these requests via timers/stats/valves etc..

Then one or more sources to keep the heat store topped up!

e.g. If the heat store is cooling down oil burner needs to fire up to re heat it.

The log burner will always top up the heat store when its burning... 

and if the heat store gets too hot, then another stat & pump to dump heat back to the heating and/or towelrads...

Guinness

.

So the log burner is piped to the tank with large pipes that give gravity flow.

I assume the tank has two heat input coils, one for the log burner, one for the oil boiler.

So you light the stove, water from the stove flows by gravity and heats the tank. If that's the case, no controls needed there.

So what feeds the radiators?

If this is a "conventional" tank, then the tank is for hot water only.  "Turning on the pump" will start circulating water from the OIL BOILER to the radiators.  That won't help you dump excess heat from the tank will it?

I think (as is sadly often the case) the plumber didn't have a clue, and has plumbed it completely wrong.

Do you have enough information to try and draw out the plumbing circuit?

This maybe of interest. 

http://www.h2panel.co.uk/h2index.htm