Wiring 2 boilers together

[leenowell]

Hi,

I need to complete the wiring on a 2 boiler system with several heating zones, UFH, secondary return loop etc. Each circuit has a 2 port motorised valve controlled by timers/ prog room stats and the relay side of these valves all return back to fire the boiler once opened. I have wired it all up to one of the boilers and it is all working fine. My question is.... Can I simply wire the second boiler in parallel with the first? I was thinking that the valves prevent any backfeeding anyway and the end result is that I need both boilers to fire if anything calls for heat?

thanks in advance

Lee.

 

[truckster]

The only problem you may have is if there are two or more pumps, you would need to separate them to prevent them pumping against a closed valve

 

[Short Circuit]

Lee, i did one a couple of days ago, similar set up except it was two boilers adjacent where one does the hot water and 2nd foor, then the other boiler does the lower two floors. Ended up with 2 rf stats/programmers, 2 valves on one and the other had one stat and a seperate programmer - just to top it off there was a pump on the hot water system too which is via a seperate programmer. That looked complicated at first but it was fairly straight forward. I agree with Truckster that you may end up with one boiler pumping against a closed valve! How has the heating engineer designed / installed the pipework - can you have one boiler for the UFH. Seems strange to me to have 2 boilers on the same system but i wouldnt class myself as an expert with heating. I have done quite a few UFH systems on large houses and never had the 2 boliers on those

 

[leenowell]

Hopefully this reply will get through.....

Hi Both.

Thanks very much for your replies. The reason for 2 boilers is that 1 domestic one was not large enough and 2 domestic was about the same price as 2 commercial so at least if 1 broke down you had the other....

In terms of the pumps, the UFH pumps are wired to the relay side of the motorised valves (1 per circuit) so should stop when the call for heat stops for those zones. The boiler is also wired this way (ie to the relay side of all the motorised valves in paralllel) so should in theory be ok. However, I did discover that the boiler pump continues for a little while after the call for heat has gone to remove the heat from the heat exchangers! Checking with the plumber, he has put in a "heat synch" loop so if all the valves are closed, this last bit of boiler pump will circulate the water around this loop of pipe.

Does this sound OK?

thanks again

Lee.

 

[truckster]

Sounds ok to me if the plumber is happy this will disipate the latent heat otherwise the boilers will be continually locking out.

 

[praxiscnc]

[FONT=&quot]If the two boilers are plumbed into the same primary flow and return pipe work, and the switch wire from the 2 port motorised valves is feeding both boilers and pumps directly, then I can’t see a problem. As you say, the control wire from the valve is likely to be isolated via relay or more likely micro-switch.

The short pump over-run is probably down to the motorised valves being equipped with micro-switches, not relays, the micro-switch is activated by the mechanical movement of the valve so the pump may over-run until the valve has got close to finishing it’s movement.

If this is the case, such a short over-run would be unlikely to help dissipate latent heat.
If that’s an issue, the heating engineer should know, and you may need to install a delay relay to allow the pumps to over-run by sufficient time.

The heating engineer should know how he needs the system to be controlled via your wiring.

I spent a year or so doing nothing but boiler control wiring and a lot more over my 10 years of electrical work, but this was a long time ago! and the valves may have changed, although I doubt it.

Hope this helps.

[/FONT]

 

[Craiggggg5]

We link 2 boilers together alot, best to fit 2 relays and then fit a switch / spur per boiler then when 1 boiler goes faulty you can turn the switch spur off.What make and model boilers have you fitted, some boilers need wiring differently to ensure you don't back feed the boilers or still supply the boiler if the internal fuses have blown.If you get stuck I can email you a drawing from work.Yours

 

[steve44]

thanks