Furthest radiators not getting hot

[windsortg]

I have a 12-year Vaillant ecoTEC Plus 438 condensing boiler that is used to heat up 19 radiators.

When the heating is turned on at the start of the morning, all radiators become hot with the 3 furthest radiators from the boiler being last to heat up. Once the set temperature on the room thermostat has been reached, the boiler turns off as expected.

When the room temperature drops and the room thermostat fires the boiler, the three furthest radiators only become luke warm, not hot like the other radiators. We have not had this problem in the past, only since yesterday since we have turned on our central heating.

Can anyone advise why this is happening and what can be done to resolve this problem? Nothing has been altered to cause this to happen.

 

[picasso]

Sounds like the pump is on its way out.

 

[windsortg]

Thanks. Would you definitely say the pump is on its way out? I would hate the change the pump and then find the problem still exists.

 

[terryplumb]

Do all rads have TRV'S ( thermostatic radiator valves)? If so close down The TRV on a couple of rads that heat up first ,and see if your problem ones now operate as they should.

 

[windsortg]

Thanks. I will try that. One thing I have noticed is that from the 2 pipes (which I assume are the flow & return pipes) that come down from a bedroom into the lounge (these 2 pipes feed the three furthest radiators), one of these pipes is hot but the other is luke warm. Does that signify anything?

The other thing I have noticed is that the pump is more than warm to the touch but not too hot that you cannot touch it.

 

[terryplumb]

Indicative of poor flow through the rads it supplies.

 

[dilalio]

Could be the pump is weakening as said.
Could also be that the furthest rads from the pump have sludged up due to distance from pump resulting in less velocity to get sediment back into suspension.
Could also be a combination of the above.

 

[dilalio]

Replace the 12 year old pump - doesn't owe you anything, or take the rads outside and flush them through.

Or do both.

 

[dilalio]

Nothing has been altered to cause this to happen.

Except 'time'

 

[windsortg]

Thanks again. The pump itself is 10 years old (photo attached). Would it make sense to replace the pump with the same model?

 

[Bouy]

As an aside have you checked what speed setting the pump is set at 1,2 or 3. If its not 3 turn it up a notch. And as suggested turn off the other radiator TRVs (all of them)

 

[windsortg]

Thanks. I will go about reducing some of the TRVs when I get a chance. If this increases the heat of the furthest 3 radiators, what would I then need to do?

The pump is already on the highest speed setting (setting 3)

 

[terryplumb]

Thanks. I will go about reducing some of the TRVs when I get a chance. If this increases the heat of the furthest 3 radiators, what would I then need to do

Balance the system

 

[dilalio]

If this increases the heat of the furthest 3 radiators, what would I then need to do?

If sediment then focusing the pump power on these rads may get it moving again, and restore full circulation. If they go cooler after bringing other rads back online, then I'd replace the pump.

 

[windsortg]

In fact, I have 20 rads of which 11 have TRVs (including the 3 rads that are furthest from the boiler). The rest are made up of 4 towel rads and 5 normal rads that do not have TRVs fitted.

Later today when the heating is about to be turned on, I will turn down the 8 TRVs (excluding those that are furthest from the boiler) to see if the 3 rads furthest from the boiler heat up efficiently. Can someone advise how long I should wait to see if these 3 rads heat up efficiently?

One thing I noticed this morning is when the heating came on, the 3 rads furthest from the boiler did heat up effectively. Would this mean anything significant?