Central heating pump and boiler

[nut&bolts]

The house has a gravity heating system. I replaced an old failing pump Grundfos UPS 15-50 (130) with Grundfos UPS3 15-50/65 130

I have drained the system and bleed the radiators for air.

The problem is that since replacement of pump boiler Glow warm (about 15 years old) comes on for about 5 minutes and then keeps cutting off and comes back on for 2 to 3 minutes and then goes back off and so on. I have tried all three speeds at pump but doesn’t seem to make a difference.


Is the pump incompatible? . I read in boiler manual that difference between flow and return should be 11 degrees. How do i set this and can this be the cause for above
.What could be the cause and how shall I proceed?

 

[John.g]

Are you sure that its running in the correct mode as these pumps have several modes of operation, constant curve speed 2 may be the most appropriate for your system, you can't post photos yet, (<10 posts) but if you post the exact model you have and which LEDs are illuminated then should be able to see what mode its in.

 

[nut&bolts]

Are you sure that its running in the correct mode as these pumps have several modes of operation, constant curve speed 2 may be the most appropriate for your system, you can't post photos yet, (<10 posts) but if you post the exact model you have and which LEDs are illuminated then should be able to see what mode its in.

It have it is constant curve speed 2, where it runs better than other speeds. Boiler does heat the water but keeps cutting off. The boiler is Glow warm ultimate 50BF

 

[king of pipes]

As above is it set to a constant speed setting ? Vented of air ? and installed to pump in the correct direction of flow ? Kop

 

[nut&bolts]

As above is it set to a constant speed setting ? Vented of air ? and installed to pump in the correct direction of flow ? Kop

Yes, I double checked all these as mentioned above. The diecrtion of arrow is correct and as in old pump. Vented air few times over two days. Also ran the pump on setting three for 30 mins three times on constant pressure to remove any possible air...
The constant speed is second green light on the pump

Is it worth changing any temperature settings on the boiler? Would the flow and return temprature contribute to the problem

 

[John.g]

If you have the old pump settings, then I would match the new pump to as close as possible, you said the old pump was failing??, was it getting noisy or what?.
Here is my link to the UPS3 which it states is controlled by a PWM signal.

If this is the pump then CC 2 is 5M which I would consider far too high for a open vented system as it can draw in air and play havoc with heat transfer, would suggest CP1 = 3M constant or PP2 which is 3.8M but will probably modulate to 2/2.5M at the required flow rates.
Also check your header tank vent etc for any air ingress or water movement in the tank at the CC2 setting.

Edit. Setting mode below which shows second green as CC2 which at 4.2M should be a reasonable setting one would think but try those other modes as well in case 4.4M is excessive as well.

 

[nut&bolts]

The oldd pump was making noise. I think it was about 15 years old. This one is quiter.
Are you suggesting that UPS 3 is not compataible ?. PWM signal. Should I be looking at some other parameter
I spoke to a plumber, this morning and he thinks boiler is overheating suggested that system may need power flush...

 

[John.g]

The UPS 3 should be quite compatible, the PWM is a external signal so no worries as not being used in your mode(s).
The boiler may be overheating but why should this occur just because you drained down the system and replaced the pump, was the system water dirty. Generally one might expect pump over in the vent with a choked system, you could just drain approx 5 litres of water somewhere and see if the ballcock is making up fairly fast as this will prove that there isn't a blockage in the cold feed.
Is there any way you can measure the pump power as this can be very revealing re blockages as the flow can be derived from the pump curves.

 

[king of pipes]

Probably best to employ a plumber for a visit to diagnose the fault you have covered the basic stuff bud winter is on its way . Regards kop

 

[steadyon]

you've probably already checked this, but were both pump valves fully opened after changing the pump?

 

[nut&bolts]

Probably best to employ a plumber for a visit to diagnose the fault you have covered the basic stuff bud winter is on its way . Regards kop

Thanks . Tommorow afternoon plumber is coming. I will let know what's the reason if he finds

 

[John.g]

One could nearly write a small book on the issues with vented systems on just changing the circ pump, everything above seems to have been done logically, I still have a doubt re Hx blockage as the boiler gets over the ignition stage where the firing rate is ~ 75% and continues to run for 5 minutes or so, at least initially. If the boiler is/can modulate down to say 5 kw then it only requires a flow rate of 3.5 LPM to maintain a 20C rise through the boiler, if its non modulating then a very good chance that a partly blocked Hx can cause the problem.
But as KOP says, almost time to call in the experts.

Edit: Just saw your post.

 

[nut&bolts]

I had a gas plumber look at the boiler. He said that gas valve and thermostat in the boiler was not working. He changed these and problem remained the same. He then said to change the boiler.

After that another plumber suggested to re-drain the system and refill. Also to t to put X400 to dissolve sludge and this was done. Since the there is no more short cycling. Boiler is running better and heating good the radiators and water.

One problem is still there is that, after switching off the controls to heat the water. The boiler keeps coming on randomly for short periods ( a minute and two).The hot water gets very hot and stays very hot . The controls are off and pump remains off.

I have reduced the boiler flame also the temperature on water cylinder thermostat to about 52. The problem remains.

What could be the problem?. Shall I try replacing the cylinder thermostat (could be spoiled)?

 

[king of pipes]

Zone valve would be the first thing to check don't just swap bits get it diagnosed properly . Kop

 

[John.g]

I had a gas plumber look at the boiler. He said that gas valve and thermostat in the boiler was not working. He changed these and problem remained the same. He then said to change the boiler.

After that another plumber suggested to re-drain the system and refill. Also to t to put X400 to dissolve sludge and this was done. Since the there is no more short cycling. Boiler is running better and heating good the radiators and water.

One problem is still there is that, after switching off the controls to heat the water. The boiler keeps coming on randomly for short periods ( a minute and two).The hot water gets very hot and stays very hot . The controls are off and pump remains off.

I have reduced the boiler flame also the temperature on water cylinder thermostat to about 52. The problem remains.

What could be the problem?. Shall I try replacing the cylinder thermostat (could be spoiled)?

If you have a S plan system you will have a number of motorised valves, its possible that one of these (hot water?) has developed a fault and the end switch (which fires the boiler) is still made with the valve de energised, the boiler will then keep firing now and then if the valve is closed or almost closed,, but the circ pump should still run for these firing periods.

 

[nut&bolts]

If you have a S plan system you will have a number of motorised valves, its possible that one of these (hot water?) has developed a fault and the end switch (which fires the boiler) is still made with the valve de energised, the boiler will then keep firing now and then if the valve is closed or almost closed,, but the circ pump should still run for these firing periods.

If you have a S plan system you will have a number of motorised valves, its possible that one of these (hot water?) has developed a fault and the end switch (which fires the boiler) is still made with the valve de energised, the boiler will then keep firing now and then if the valve is closed or almost closed,, but the circ pump should still run for these firing periods.

It is a Y plan. Only three port valve. There does not appear to be a zone valve I can see. I double checked ? The pump remains off and so the electronic water timer/control
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So, i need to check the three port valve to start with.
How do i do that ?.

 

[John.g]

You say the hot water gets very hot, do you mean the hot water from the hot tap or the boiler water?. I am not familiar with the 3 port valve but it may stay in the hot water position when de energised and if the boiler then fires but without the circ pump it could circulate the water by gravity, and why is the boiler firing up randomly and not starting the circ pump I wonder.
I think these 3 way valves stay in the last selected position if working properly so suggest selecting CH mode for a few minutes then switch off (CH) and see if boiler still fires randomly, presume circ pump is working normally otherwise.

 

[nut&bolts]

Before any problems, the pump would only start when I switch on the controls to call for heating the water. The pump will go away when the controls are switched off.
It is still the case with the pump but boiler keeps coming on randomly for a minute or two. I don't know why this is the case ?. As a consequence It is the water in the taps that is getting extremely hot....

 

[John.g]

Strange alright, possibly looks like 3 way valve problem, maybe worth trying it above in CH mode for a few minutes but maybe its still doing this when CH shuts off normally?.

 

[exedon2]

Maybe cylinder stat? Remember when programmer off stat will have a live feed from the hot water off on programmer? Thats why your forever finding earth used as a carrier on cylinder stats on Y plan.

 

[John.g]

Quite possible but why isn't the circ pump running during this random period.

This link is excellent but it takes me a long time to absorb it each time I look at it.

Y Plan central heating system

Y-plan central heating system operation and wiring diagram

www.flameport.com

 

[exedon2]

True enough boiler and pump should be linked unable to run independently

 

[nut&bolts]

Quite possible but why isn't the circ pump running during this random period.

The pump only runs when mannualy switch on through controld or it is on timer. In my system it never was running when controls were off.

Interestingly, the central heating works okay. when I switch it off from thermostat or controls, It goes off but hot water keeps getting hot and hotter
[automerge]1603318915[/automerge]
To clarify, when I switch on central heating or hot water to get heated in the cylinder, then only the pump and boiler runs. When the controls are off, the pump does not switches on, despite boiler coming on randomly

 

[John.g]

Have to sleep on it tonight.
[automerge]1603355506[/automerge]
Just a few more comments.
You confirm that system works in all three modes, ie, CH only, HW only, and CH&HW.
Also that when you have CH only selected and it switches off then the boiler (only) will fire randomly but heats the HW cylinder.
The valve is supposed to stay in the last selected mode (except if whole system is powered off where it will revert to HW only) so this doesn't seem to be happening as the random boiler firing is heating the cylinder and should be trying to heat the rads if CH only had been selected.
The only suggestion I can make just now is to shut off the power then remove the orange wire temporarily then restore power and with both CH and HW off see if the boiler still randomly fires.

There was a problem some years ago with the UPS2 pumps which was was damaging contacts etc but I think was solved by supplying a suppressed pump cable but as your pump is new then can't see this as causing the problem.

 

[SJB060685]

I have read all comments but forgive me if I've missed something.
The wiring on these systems is simple, by no means as complicated as some modern systems.
By the sounds of it something is not wired up right.
When the room stat or cylinder stat calls for heat the motorised valve does its thing internally and the boiler and pump are brought on. Both lives to each are tapped into the connector with the orange wire from the three port.
Another possibility no one has mentioned but I doubt is the case is is there a frost stat somewhere?
When wired correctly the boiler and pump should only be energised when theres a demand and it comes from a switch live, there should no link to any other live at all.