Radiators not getting hot enough, pump on constantly-help!

bristolboy25

You can get stuff so clean out the system, leave it in then drain a few days later ans all the sludge will come out. My OH done ours and all this sludge that looked like frog spawn came out, it was vile. It all works good now but just done extension and rads not on in there yet so I am cold anyway!

moneysavingplumber

wizzer wrote:

So, I've just had a Glow worm 24hxi installed which has a max setting of approx 82C.

If I set my cylinder temp to 55C (recommended hw temp?) then the boiler will need to be set to 75C to avoid boiler over-run? I ask because I have had problems with a continuously running pump possibly because the boiler thermostat has not been set high enough?

Thanks

Cylinder stat should be set to 60, the temperature differentials for the boiler flow and return should have been set by the commissioning engineer whilst balancing the system. Check the blue 'Benchmark' book and see what has been entered for that piece of data.

wizzer

moneysavingplumber wrote:

Cylinder stat should be set to 60, the temperature differentials for the boiler flow and return should have been set by the commissioning engineer whilst balancing the system. Check the blue 'Benchmark' book and see what has been entered for that piece of data.

Flow Temp says 80C & Return Temp says 62C.

moneysavingplumber

wizzer wrote:

Flow Temp says 80C & Return Temp says 62C.

The differential should ideally be twenty degrees but this is really difficult to achieve accurately, so it's not bad, if your digital display temperature says 75 degrees then in theory it should be coming back at around 55.

wizzer

moneysavingplumber wrote:

The differential should ideally be twenty degrees but this is really difficult to achieve accurately, so it's not bad, if your digital display temperature says 75 degrees then in theory it should be coming back at around 55.

I may be confusing myself. The pump seemed to be running constantly when the cylinder stat was set at 55C and the boiler stat at about 70C presumably on the return. By turning the cylinder stat down to 50C (which still seems more than adequate for HW) then this is a temp diff of about 20C which seems to stop the pump running on indefinitely.

Is this how it's meant to work or is something wrong somewhere?

Thanks

djohn2002uk

wizzer wrote:

I may be confusing myself. The pump seemed to be running constantly when the cylinder stat was set at 55C and the boiler stat at about 70C presumably on the return. By turning the cylinder stat down to 50C (which still seems more than adequate for HW) then this is a temp diff of about 20C which seems to stop the pump running on indefinitely.

Is this how it's meant to work or is something wrong somewhere?

Thanks

moneysavingplumber is the best person to answer this but I would add that I read somewhere a couple of weeks ago that your hot water needs to be 60 degrees. Anything below and legionella bacteria can breed.

wizzer

djohn2002uk wrote:

moneysavingplumber is the best person to answer this but I would add that I read somewhere a couple of weeks ago that your hot water needs to be 60 degrees. Anything below and legionella bacteria can breed.

BS6700 recommends 55 degrees apparently.

moneysavingplumber

I wouldn't worry about BS6700, djohn2002uk is right. The recommendation is likely to be raised to 70 degrees in future with a thermal mixing valve being compulsory in new properties because there is evidence, apparently, that legionella can still proliferate at 60. Limescale is also more of a problem at below 60 degrees.

wizzer

wizzer wrote:

I may be confusing myself. The pump seemed to be running constantly when the cylinder stat was set at 55C and the boiler stat at about 70C presumably on the return. By turning the cylinder stat down to 50C (which still seems more than adequate for HW) then this is a temp diff of about 20C which seems to stop the pump running on indefinitely.

Is this how it's meant to work or is something wrong somewhere?

Thanks

MoneySavingPlumber
Are you able to respond on this one please?

moneysavingplumber

The boiler and pump are not really supposed to cycle on a system where the by-pass and lockshield valves have been set and balanced correctly. If it is working and sized correctly then the boiler should stay lit (more or less) until the room and cylinder stats are satisfied. Obviously a higher temperature on the stats will mean you will burn more gas. If you want to set your cylinder stat at 50 that is entirely up to you, but the current recommendation is 60.

If the flow temperature at the cylinder coil inlet (flow) is at around 60-65 degrees, the return should be 40-45 degrees. This is usually achieved by a lockshield valve on the cylinder return immediately upon exiting the coil which is restricted to achieve the differential. The system by-pass will usually be set up whilst the system is in hot water mode only so as to be sure to give the correct differentials between boiler flow and return whilst the system is on minimum load. Radiator valves need to be set in the same way.

If you are saying that the cylinder stat is not being satisfied at 55 degrees then you may need to check the calibration of that and the boiler stat. Ultimately, all this type of thing is the responsibility of the people that fitted the boiler under Benchmark and the Part L building regulation. I assume the installation was registered with building control via Corgi. If not, it should have been, and if it was, Corgi may select you for a spot-check to see if it's been installed correctly, I know they've contacted a few of my customers.