Heating Problem - Potterton Boiler - Micro Bore System

[alanprorib]

The problem I have is the boiler will lift the temperature of the radiators to between 50-60 degC, then goes to standby and the returns and hold the radiators at the this temperature for a while. After a short period of time the goes back into standby mode then lights up again for 2-3 minutes and back to standby. At this point the radiator temperature drops down to temperatures 23-35degC.

The room temperature is 19 degC measured with digital thermometer and the wall thermostat is at 25 degC.

The temperature at the pump is 43 degC. The pump is a new Grundfos 15/15 operating in position 3.

The boiler thermostat is set a number 4.

If the boiler thermostat is set to maximum the over temperature button pops out.

If I turn the hot water temperature up to 70 degC and switch on the demand for hot water the boiler lights and will lift the radiator temperature back up to 50-60 degC.

The following readings were taken with the central heating switched on and hot water off.

At the start and switching the boiler
Elected Rad = 20 DegC
Room Temp = 18 DegC
Room Thermostat = 30 DegC
Boiler Left Pipe (facing boiler) = 30 DegC
Boiler Right Pipe (facing boiler) = 43 DegC
Boiler Setting = 4

After 10 minutes
Boiler Left Pipe (facing boiler) = 49 DegC
Boiler Right Pipe (facing boiler) = 45 DegC
Elected Rad = 40 DegC
Room Temp = 18 DegC
Room Thermostat = 30 DegC

After 55 minutes
Boiler Left Pipe (facing boiler) = 56 DegC
Boiler Right Pipe (facing boiler) = 40 DegC
Elected Rad = 29 DegC
Room Temp = 18 DegC
Room Thermostat = 30 DegC

After 80 minutes
Boiler Left Pipe (facing boiler) = 57 DegC
Boiler Right Pipe (facing boiler) = 29 DegC
Elected Rad = 25 DegC
Room Temp = 18 DegC
Room Thermostat = 30 DegC

After 92 minutes
Boiler Left Pipe (facing boiler) = 54 DegC
Boiler Right Pipe (facing boiler) = 32 DegC
Elected Rad = 20 DegC
Room Temp = 18 DegC
Room Thermostat = 30 DegC


The following readings were taken with the central heating switched on and hot water on.

Boiler Left Pipe (facing boiler) = 58 DegC
Boiler Right Pipe (facing boiler) = 53 DegC
Boiler Setting = 4
Elected Rad = 40 DegC
Room Temp = 18 DegC
Room Thermostat = 30 DegC

The readings for the boiler feed and return pipes were taken directly between the rubber grommet and the wall of the pipe.

All readings were taken with a new digital probe.

Once the hot water is turned on the boiler will and deliver good central heating with consistency. If the hot water is switched off the problem returns.


Any advice would be very much appreciated.

 

[kayedee]

If this is a system utilising a mid position valve sharing hot water and central heating, symptoms you describe point to the auxillary switch on the valve not operating (which switch on boiler and pump) on call for central heating. They are prone to sticking, if you operate it manually a few times using the manual lever it should free it off.

 

[alanprorib]

If this is a system utilising a mid position valve sharing hot water and central heating, symptoms you describe point to the auxillary switch on the valve not operating (which switch on boiler and pump) on call for central heating. They are prone to sticking, if you operate it manually a few times using the manual lever it should free it off.

The system has two Honeywell motorised valves and not a three port valve.

I have operated themanual levers on the motorised several times whist the pump has been running and not running.

The next step will be to take the motorised valves out a check they opening fully.

For two days now I have been bleeding the system by venting each radiator and the balancing radiator.

Whist the hot water is on the all radiators get hot hot.

 

[kayedee]

OK, so I can assume that one of the valves turns of flow to hot water cylinder and the other the radiators, on call for CH from the time programmer the live wire goes to the room thermostat, if this is turned up above the room temperature, you should hear the radiator valve open, which in turn activates a micro switch in the valve when it has opened, which turns boiler and pump on.
let me know how far in the chain you can get.

 

[alanprorib]

OK, so I can assume that one of the valves turns of flow to hot water cylinder and the other the radiators, on call for CH from the time programmer the live wire goes to the room thermostat, if this is turned up above the room temperature, you should hear the radiator valve open, which in turn activates a micro switch in the valve when it has opened, which turns boiler and pump on.
let me know how far in the chain you can get.

If I operate the room thermostat by switching the temperature up the following happens:

1) CH Motorised valve opens (checked by using the manual lever)
2) Grundfos pumps starts and runs
3) Boiler starts and runs
4) System running 1-2degC temperature difference either side of the CH motorised valve.

If I operate the room thermostat by switch the temperature down the following happens:

1) CH Motorised valve closes (checked by using the manual lever)
2) Grundfos pumps stops
3) Boiler stops

Repeat the change up of temp on room thermostat and all works fine.

The CH got all of the radiators hot, the boiler stops but the pump continues to run. The temperature of the radiators drops and stays warm until I switch off the CH and restart with the HW first then start the CH.

All radiators get hot again.

If I start the CH first then start the HW the radiators do not get hot only warm.

When the timed program starts both CH and HW the radiators get hot and remain hot all of the time the HW channel is switched on.


At the moment due the low outside tempaerature I running both the CH and HW together on the timer.

 

[kayedee]

Did you start your trial with just CH selected on programmer?
and what model boiler is it?

 

[alanprorib]

The boiler is a Potterton Netaheat Profile 60e.

The programmer is a Potterton EP 2000.

The room thermostat is Honeywell wall mounted simple unit.

Yes, the trial was started with CH only.

After about 30 mins the radiator temperature drops but the pump and boiler continue to run. The water flow temperature through the motorised valve is very hot but the flow pipe into boiler is warm. At this time the HW motorised valve was closed (no hot water flow through the valve).

Once I established the CH side of the system was not working correctly, I switch on the HW program and the hot water did not flow through the HW motorised valve and the radiator temperature did not improve.

I then switched both CH and HW off and then restarted both programs again the radiators got hot and have remained hot 5 hours. Radiators will work correctly if both CH and HW programs are switched on.



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• alanprorib
• 11 Dec 2012
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• alanprorib
• 11 Dec 2012
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• alanprorib
• 11 Dec 2012
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• alanprorib
• 11 Dec 2012
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• alanprorib
• 11 Dec 2012
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[kevplumb]

nicrobore
first thought from me FWIW is lack of flow
that set up is from the dark ages
but it should still work

 

[kayedee]

Before we go any further, when did this problem first happen, and was it gradual (where you are unable to give an acurate timescale).
And do you have a voltmeter.

 

[alanprorib]

The problem was recently identified after replacing the main pump from a euramo mxl 180 to a grundfos Selectric 15-50.

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• alanprorib
• 11 Dec 2012
• 1

The pump was replaced because it was noisy and viabrating, even when operated at the low speed. There was also a lot noise (kettling) from the boiler. All the noise stooped once the pump was changed and the chemical was added to the water.

I have lived in the house for two years and the heating as never been very good, the radiators have never appeared to deliver heat. With the HW water on the radiators get hotter than ever noticed before. The radiators are still the originals and appear to be not the correct size for the rooms.

After draining the whole system, changing the pump and feel with noise reducing chemical, the whole system was bled of over several days. It wa during the initial bleeding of air that it was noticed that the boiler and pump were running but the radiators were not getting hot. The boiler also tripped on over temperature despite the return pipe was only warm. At this point I switched on the HW channel and the motorised valve opened and the ch system got hot. Even now if the boiler is set to maximum temperature the boiler will operate for a period of time and then over heat and trip out on over temperature.

With boiler set at mark 4 the HW Cylinder thermostat 70degc) and CH work well. However the heating system will never raise the lounge temperature above 22 degC against and outside temperature of 0degC.

I do have both an analogue and digital volt meters.

 

[Agile]

Who replaced the pump?

Assuming the picture is the right way up then the motor head is upside down!

Was that a substandard DIY attempt or a nupty professional?

Tony

 

[kayedee]

With that information it is probably a hydrolic problem.
Is the pump in the right way round, flowing away from boiler.
Was the system flushed till clean when you drained the system.
If so how bad was it.
Was each radiator flushed through in turn by turning all other radiators off except for the flushing radiator.
Was the boiler also flushed out by closing all radiators.
Comfortable room temperatures at low outdoor temperatures below zero will not be achievable unless the boiler flow is operating around the designed 82 degrees C.

 

[alanprorib]

The system was never drained and flushed by closing each radiator.

Originally the system was drained for the purposes of replacing the pump and installing the required distance piece.

The pump was installed with the flow arrows pointing up, the flow comes in at the bottom and goes out at top onto the CH and HW motorised valves. You can see from the photograph the Grundfos label is the correct way up.

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• alanprorib
• 12 Dec 2012
• 1

The colour of drained water was a golden brown colour with some black towards the end of the draining.

The chemical was added to reduce the kettling noise.




I have today installed an automatic bleed valve to the dog’s leg vent pipe just after the HW motorised valve. Prior to this, was a manual valve and it has always released air when manually vented. The hope is the automatic will stop any requirement to bleed the air from the system.

To install the automatic vent, the system was drained of the chemical and the colour of the water was a light golden colour (pale urine).

The system has now been refilled and bled at each radiator.

The pump was used to circulate water with the boiler off and stopped each time of bleeding the system.

I will now let the system run overnight and bleed the whole system again tomorrow.

The room temperature problem is not due to water circulating problem, it is due to the fact the previous owner of the property has extend and built on a conservatory and not increased the radiator size to accommodate both increase in volume to be heated and the heat loss due to the significant increase in the glass area. I have checked with two different calculators and the radiators should be at least double the size.

 

[kayedee]

The CH got all of the radiators hot, the boiler stops but the pump continues to run

At this point can you determine why the boiler stopped, is it the boiler control stat satisfied?

 

[Agile]

The pump was installed with the flow arrows pointing up, the flow comes in at the bottom and goes out at top onto the CH and HW motorised valves. You can see from the photograph the Grundfos label is the correct way up.

The label can be rotated to any orientation that you choose!

Most would have advised using a 15-60 pump on a microbore system.

Tony