Gravity hot water. Gas condensing boiler. 4 bed detached.
Radiators balanced. System bled. House slow to heat. Low return temp to boiler. Pump intermittent cavitation.
I would appreciate some advice on trouble shooting my central heating. It's slow to heat up and the pump is intermittently very noisy once the system heats up.
My central heating circulation pump is making what sounds like a cavitating noise. The noise is intermittent and starts after the system has been on for a while. See attached video. The pump is quite old (British Gas Multihead G, part number 59506180). Maybe twenty years old. The speed is on the highest of its three settings.
I have 15 radiators and a mix of 15mm and 10mm tails. The main flow and return lines at the boiler are 28mm. I've recently balanced the radiators as some weren't heating up at all. All the radiators now heat up at the same rate. There are no cold spots on the radiators. However, the house heats up very slowly. It increases in temperature by about 1°C per hour. So it takes around 5 hours to go from 14°C to 19°C. It struggles to get above 20°C (4 bed detached).
The boiler is a Worcester Greenstar 24 Ri. I don't know its age, but I would guess around ten years old. It's rated at 24kW. I've monitored the gas consumption at the incoming gas meter and it is only consuming the equivalent of around 12 kW when the system should be running at full load to achieve the thermostat set point temperature (20°C).
The flow temp is set to max on the boiler. I haven't measured the temperature on the flow line, but from touch it seems around 70°C. The return line is around 15°C. That indicates a flow rate of around 3 litres/min (0.05 litre/sec), assuming 12 kW and a dT of 55°C.
I appreciate I could have a few problems but I was hoping for some direction on where to start. The boiler is consuming around 1/2 of its rated capacity. The boiler is serviced annually so fouling shouldn't be that bad. There is a filter on the return line and the water out of the bleed points looks clean.?
If the pump isn't delivering the mass flow then the boiler can't run up to capacity otherwise it would overheat the water.
The pump may not be delivering the flow rate because it is faulty or the system resistance could be too high? The last radiator in the circuit is full open, but I had to close off the lock shields on the other radiators quite a bit to balance the system. So the system resistance could be significant.
Do I take a chance and change out the pump. E.g. for a more modern Grundfos UPS3 15-50/65. The UPS3 has a greater flowrate at a higher head so could help if the system resistance is the issue.
I'm not sure a new pump would solve my cavitation issue though? The system is vented so I can’t increase the pressure other than to fill up the header tank in the loft, which hasn’t solved the cavitation.
Any help appreciated.
Radiators balanced. System bled. House slow to heat. Low return temp to boiler. Pump intermittent cavitation.
I would appreciate some advice on trouble shooting my central heating. It's slow to heat up and the pump is intermittently very noisy once the system heats up.
My central heating circulation pump is making what sounds like a cavitating noise. The noise is intermittent and starts after the system has been on for a while. See attached video. The pump is quite old (British Gas Multihead G, part number 59506180). Maybe twenty years old. The speed is on the highest of its three settings.
I have 15 radiators and a mix of 15mm and 10mm tails. The main flow and return lines at the boiler are 28mm. I've recently balanced the radiators as some weren't heating up at all. All the radiators now heat up at the same rate. There are no cold spots on the radiators. However, the house heats up very slowly. It increases in temperature by about 1°C per hour. So it takes around 5 hours to go from 14°C to 19°C. It struggles to get above 20°C (4 bed detached).
The boiler is a Worcester Greenstar 24 Ri. I don't know its age, but I would guess around ten years old. It's rated at 24kW. I've monitored the gas consumption at the incoming gas meter and it is only consuming the equivalent of around 12 kW when the system should be running at full load to achieve the thermostat set point temperature (20°C).
The flow temp is set to max on the boiler. I haven't measured the temperature on the flow line, but from touch it seems around 70°C. The return line is around 15°C. That indicates a flow rate of around 3 litres/min (0.05 litre/sec), assuming 12 kW and a dT of 55°C.
I appreciate I could have a few problems but I was hoping for some direction on where to start. The boiler is consuming around 1/2 of its rated capacity. The boiler is serviced annually so fouling shouldn't be that bad. There is a filter on the return line and the water out of the bleed points looks clean.?
If the pump isn't delivering the mass flow then the boiler can't run up to capacity otherwise it would overheat the water.
The pump may not be delivering the flow rate because it is faulty or the system resistance could be too high? The last radiator in the circuit is full open, but I had to close off the lock shields on the other radiators quite a bit to balance the system. So the system resistance could be significant.
Do I take a chance and change out the pump. E.g. for a more modern Grundfos UPS3 15-50/65. The UPS3 has a greater flowrate at a higher head so could help if the system resistance is the issue.
I'm not sure a new pump would solve my cavitation issue though? The system is vented so I can’t increase the pressure other than to fill up the header tank in the loft, which hasn’t solved the cavitation.
Any help appreciated.
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