Dual system - 2 pumps - operation question?

oinkely

Hi all,

I am hoping to get a some advice on my central heating system. I have oil fired central heating and also a solid fuel stove with a back boiler.

the stove was put in about two years ago and has been working really well. At the time the plumber who connected it up mentioned that we should not run the pump for the back boiler at the same time as the central heating pump. As i was busy with other things (a new baby) at the time i did not question why.

we have our central heating timed to come on at various time throughout the day, though when i am home all day i usually turn it off altogether as with a fire burning in the stove the house is lovely and toasty, so no need for the central heating.

Every now and then though i forget to turn off the central heating and it comes on when the fire is lighting. on the few occasions that it has happened there have been no obvious ill effects, no noisy pipes etc.

so i guess i am wondering how i go about establishing if it is OK to run the system with both pumps on at the same time, as one particular rad is much hotter with the pump for the back boiler running, and rarely heats up with the central heating. so in a way, the two pumps running a the same time is beneficial.

Sorry for the long post, just trying to give as much info as required and please ask for more if you need it.

many thanks for any replies.

Plombier

Its ok to run both pumps at the same time if the system is installed correctly.

Sparkpea

I've always been taught not to run the 2 systems at once unless a baker system or similar is installed as its unsafe otherwise

Plombier

Its just two boilers in parallel, nothing special.

Sparkpea

suppose it depends if both pumps are on the flow or return or one of each, like if all the pipes are connected the same

ntpm

The plumber was probably worried about "pitching". This is when the hot water is forced up the Open Safety Vent (OSV commonly wrongly know as expansion pipe).
This happens when the system have been incorrectly designed/ installed.

If correctly installed:
The oil heating should be zoned with room stat with motorised for heating circuit and a thermostat with motorised valve on the cylinder.
This will not allow heat to disapated into the cylinder is the stove has heated the cylinder.

The stove will have a pipe stat and a pump which will circulate excess through the radiator circuits if the cylinder gets hot enough via bypass/ non return valves on your oil heating radiator pipework.

The two systems should be able to run independently and together.

Basically, run both system. Make sure both pumps operate and check the small tank in the attic.

oinkely

Thanks for the replies folks.

As for the systems being installed correctly - can't be certain as the house was built in the 80s and we moved in 4 years ago. Who knows what was done in the intervening years!

There are definitely no motorized valves anywhere though! The stove set up is exactly as ntpm describes. I don't think the oil system is anything like his (making a gross assumption here that ntpm is male, apologies if I am incorrect!) description though, ie no valves, no room stat etc. I did add in trv's on most of the radiators recently though.

So in essence, as long as the two pumps are pumping in the same direction then all is hunky dorey?

The oil boiler is in the shed and the pipework is easy to see. I guess if the pump is on the top pipe it is the flow and if it is on the bottom pipe it is the return?

Then I go to the pump beside the stove, with the fire off, and see if the pump there is on the pipe that gets hot first with the oil boiler on. Would this tell me if they are pumping in the same direction? I kind of think they are due to the lack of any ill effects (that i could see) when the two have been accidentally on at the same time in the past.

Thanks again for all the info.

Buford T Justice

Have you got NRV's fitted at the boiler and the stove, to prevent the boiler heating the stove, and the stove heating the boiler?

oinkely

Fingers

yes at the oil boiler - not sure at the stove (but my inclination is that there are none as the inside of the stove sometimes feels warm when you open it to light the fire after the oil central heating has been on.

Buford T Justice

oinkely wrote: »

Fingers

yes at the oil boiler - not sure at the stove (but my inclination is that there are none as the inside of the stove sometimes feels warm when you open it to light the fire after the oil central heating has been on.

You should have an NRV on that circuit too.

demanufactured

Fingers McGee wrote: »

You should have an NRV on that circuit too.

YOU CAN NOT PUT A NON RETURN VALVE ON A SOLID FUEL BOILER!!!!

Plombier

YOU CAN NOT PUT A NON RETURN VALVE ON A SOLID FUEL BOILER!!!!

On the branches off the gravity circuit connecting to the heating circuit is where it should be.

Sparkpea

as good as these forums are sometimes they are crap when people post bad advice

Buford T Justice

Sparkpea wrote: »

as good as these forums are sometimes they are crap when people post bad advice

Such as?

Sparkpea

Fingers McGee wrote: »

Such as?

was just about to edit saying that its not necessarily related to this thread, tho someone did say it was ok to bypass a boiler thermostat the other day - dangerous

Buford T Justice

Sparkpea wrote: »

was just about to edit saying that its not necessarily related to this thread, tho someone did say it was ok to bypass a boiler thermostat the other day - dangerous

Yeah, I saw that :eek: Ended up bursting two pipes in his basement as a result.

Lesson learned methinks.