turning on and off the circulating pump with boiler

bjdodo

Hello Guys

I have a firebird superq boiler, and of course the heating system contains a circulating pump as well. I am planning to buy a sophisticated thermostat and I would like to achieve to be able to turn on and off the boiler using the thermostat. As there is already a simple thermostat this aim seems easy except for when it comes to the problem of switching the circulating pump. By playing with the wiring of the boiler I can achieve two things easily:

1. The pump only runs if the room thermostat "feels" that the room is cold, i.e. when the boiler does run. This is not optimum because if the room thermostat switches the boiler on and off very often (might happen) then it would also switch the pump on and off. It means that hot water might end up cooling in the boiler and the pump for a relatively large proportion of time during heating hours and I worry about the piping of the boiler, especially I am worried about building up limescale. Anyway it seems a good idea to circulate water until it gets cooler.

2. The pump runs for 24 hours. Again not the best case, the lifetime of the pump will be reduced and it is a waste of electrical energy.

Logically I think there are these (probably) much better options:

3. The boiler turns off and the pump keeps operating for e.g. 15 more minutes. By this time the water must have cooled a lot so the pump can turn off.

4. There could be a heat sensor in the pump and if the water temperature is below a given value then the pump could turn itself off.

So my question is: are there circulating pumps that have any of there features? Can you think of any better approach? How are these things usually done?

Thank you all!! (and Happy New Year :-) )

Joe

Micky Dolenz

1 is an interlocked system, where stats control boiler directly, they by pass tme clock.

2 Not the best idea, it would effectively suck the heat out of the water in your hot water cylinder.

3 15 minutes is a bit long, but you are on the right track.

4 Pump could be controlled by pipe stat, when the pipe stat hits a certain temp, the pump kicks in,once it drops below this temp the pump stops


A pump over run and an automatic bypass valve would solve all your problems.

bjdodo

Hi Micky

Thank you for your answer! I have googled these terms and really this seems to be the solution but I am not familiar with these things so I have some questions again.

By "Pump could be controlled by pipe stat" did you actually refer to "pump over run", or are these two different things?

Where would the automatic bypass valve fit? What is closed at the moment when the burner switches off? The boiler is not, I want to circulate the hot water away from the boiler so I can't bypass it. The pump is working (?) because of the pipe stat.

Thank you again!

Joe

items

Best to keep pump separate from boiler (in a way). Your room stat might not be satisfied and calling for heat at the same time your boiler might be satisfied with boiler temperature. What happens then? Pump has to run on, no real way around it, any other way is heading towards an inefficient set up.

You can buy time clocks with built in thermostat. These clocks have multiple program options, boiler on timer, boiler on timer along with thermostat, boiler on with just thermostat, all sorts.

If you really want to get fancy, pick up a weather compensating kit. This way you'll never have to touch any controls, after you set it up, boiler will come on depending on outside temp. Hot water will have to be timed / controlled for summer months etc.

Have a pipe stat fitted so pump runs on until set lower temp is reached. Will save from possible high limit boiler lockouts, water is hot in boiler after it shuts down, its great to get that extra bit out of boiler.

If your looking at improving circulation pump, you can buy class A energy efficient pumps, they modulate depending on demand.

bjdodo

Hi,

Thank you for your answer.

"Your room stat might not be satisfied and calling for heat at the same time your boiler might be satisfied with boiler temperature. What happens then?"

Well, I am not sure how to solve it but what should happen in this situation is that the pump should carry on and the burner should switch off. But once the temperature of the water drops the pump should also stop.

"Have a pipe stat fitted so pump runs on until set lower temp is reached."

Yes, if it is really something that can be done this is what I'll choose, I am just unsure about how to connect it. If the burner is working the water should flow no matter how hot the water is. But if the burner is off water should still carry on as long as the pipe stat thinks water is hot enough. I'll have to think about the electrical circuit here :-)

"you can buy class A energy efficient pumps, they modulate depending on demand. "

What is demand in this case? Water temperature? This could be an ideal solution then.

Thank you,
Joe

items

bjdodo wrote: »

Hi,

Thank you for your answer.

"Your room stat might not be satisfied and calling for heat at the same time your boiler might be satisfied with boiler temperature. What happens then?"

Well, I am not sure how to solve it but what should happen in this situation is that the pump should carry on and the burner should switch off. But once the temperature of the water drops the pump should also stop.

"Have a pipe stat fitted so pump runs on until set lower temp is reached."

Yes, if it is really something that can be done this is what I'll choose, I am just unsure about how to connect it. If the burner is working the water should flow no matter how hot the water is. But if the burner is off water should still carry on as long as the pipe stat thinks water is hot enough. I'll have to think about the electrical circuit here :-)

"you can buy class A energy efficient pumps, they modulate depending on demand. "

What is demand in this case? Water temperature? This could be an ideal solution then.

Thank you,
Joe

Its best to leave pump alone (left wired into factory control) folks who design boiler controls etc know what they are doing, all user type control should be after main boiler control (unless options available).

Pipe stat wired correctly will over ride other controls until stat reads set temp required to turn off pump. In your boiler manual you should see some mention of pipe stat (how to wire etc)

Modulating pumps can sense load, demand etc then circulate to provide only whats required. A lot of systems now have thermo rad valves, these valves restrict / increase flow depending on room temp, modulating pump works well with TRV's or any thermo controlled zone system, less power, longer lifespan.

Micky Dolenz

bjdodo wrote: »

Hi Micky

Thank you for your answer! I have googled these terms and really this seems to be the solution but I am not familiar with these things so I have some questions again.

By "Pump could be controlled by pipe stat" did you actually refer to "pump over run", or are these two different things?

Where would the automatic bypass valve fit? What is closed at the moment when the burner switches off? The boiler is not, I want to circulate the hot water away from the boiler so I can't bypass it. The pump is working (?) because of the pipe stat.

Thank you again!

Joe

Pump over run and pipe stat are two different things but do the same thing, in your case the easiest and cheapest way to acheive it, is by using a €15 pipe stat. Basically cut into cable feeding pump and run it thorugh the stat. Fit pipe stat on flow pipe (top pipe). the stat would need a permanent live. you don't want it controlled by time clock switch live as it would power down once time clock turns off.

As items has pointed out, there are lots of clever controls on the market, the weather compenstators are a brilliant idea and one we will see alot of in the not too distance future in a domestic settting. They would be the norm in commercial buildings but for now are rare enough in homes.

I assume your have heating zones? If so, you will have stats that control motorised valves. once this stats are at temp, they shut down motorised valves, all new systems are now interlocked, so the stat in effect controls boiler. Stat is at temp, closes motorised valve, relay in motorised valve sends shut down message to boiler, by passing time clock.

If all motorised valves are shut, the pump over run will need to pump somewhere, a by pass valve is fitted between the flow and return before any motorised valves, so the pump will have a circuit to pump too. An automatic by pass valve will only open, under full pressure of pump I.E when all zones are shut. It would not allow circulation if a zone was open.

bjdodo

Hi Micky

Thank you very much for your help. We do not have heating zones so the pump over run is not necessary (heating cannot be turned off separately in the kitchen). But good to know about this problem and the solution!

Looking at the circuit diagram of the Firebird Superq I think if I connect a thermostat in parallel with the boiler to supply the pump (so that they both can turn the pump on) then the voltage from the thermostat can cause problems in the boiler (it can turn it on) so my solution is to install a relay to the output from the boiler (this thing: http://maplin.co.uk/Module.aspx?moduleno=37519 - if you know of an Irish owned shop in Galway city where I can buy such things pls let me know). I hope I won't blow up the whole thing :-)

Thank you for all your help!

Regards,
Joe

galway1973

maplin in wellpk should have it or be able to get it for you