CH Circulation

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Getting a little frustrated with my CH system.

Symptom - poor circulation, difficult to balance. 16 Rads, 3 Towel Rails. boiler on top floor. Large property (converted church). Mix of Cast iron rads and modern. Magnaclean fitted.

System is reasonably clean - only about 3 years old, and I've drained system 3 times, and flushed two suspect radiators, replumbed to simplify twists and turns to them. Have fitted new Drayton TRVs on all rads throughout. Replaced 2 undersized old rads with new.

Can now get all rads hot, individually. House is over 3 floors, and lots of the runs drop to the rads, which makes draining a bit of a sod.

If all lockshields are wide open, only about 3 or 4 rads get hot upstairs. To get any flow downstairs or to the cold rads, I have to almost close many of the other lockshields - down to .125 of a turn of 5 turns say. Even then, some parts of the circuit won't heat until I've refitted all the TRV heads (thus shutting down some rads completely).

Questions - could it be a dodgy pump (inside Vokera Linea 36HE) (it makes the right noises at the different speeds, and I can hear it pumping water). Or is it typical on a large circuit, to have to shut down so many of the lockshields down so far?

The system seems to be clean and sludge free now (there wasn't much muck in it and apart from the 2 problem rads, all the rads seem to be clean and heat properly top to bottom when isolated).

If the pump, is it ok to just buy the pump head, or do I need the whole unit?

Simon
 
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I'm no expert (one will be along shortly) but I suspect your pump will not be up to the job.
It will be a standard domestic pump, no doubt. You have 16 rads etc over 3 floors. The pump will be designed to cope with something like a 2 storey 4 bedroom house.

I might be wrong.


(I wouldn' tnormaly post to something like this but I'm wide awake and bored. Bl**dy steroids! ;) )
 
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if the pump isn't doing it's job you should find that the boiler is cycling on and off every few minutes, with very hot water on the outgoing feed even though the temperature of the water on the return feed is still cold.

OTOH if the boiler is running close to flat-out for several minutes until the returning water is also starting to feel pretty warm, chances are the pump is OK.
 
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I have a normal 2 storey house with 13 radiators and this is just
about on the limit of one normal house pump.

I suggest you zone your heating into 2 or perhaps 3 circuits each with it's own pump and controlling thermostat.

This should sort the problem.

Do you have a hot water tank? If so switch this off when the heating is on.
If not water will find it easy to shoot around the cylinder coil.
 
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I'll double check at the weekend, but i'm pretty sure it's cutting out before the return gets hot, but the flow gets hot as expected. Eventually, the return will get warm, but that's before all the radiators are getting hot. I've tried so many things, I'll try and be a little more structured and methodical to figure out what's wrong.

Appreciate it might not be ideal for the size of house, but it's what we inherited when we bought it, and with TRVs and the rough balancing I described above, it works reasonably well. It just seemed abnormal to me to have to close down the lockshield valves so far on some rads. Also I wondered if pumps degrade with time - ie, it's definitely working, but I'm not sure if it's working as well as a new one, but ideally, don't want to leap to chasing problems by switching out components one by one if I can help it.

Splitting the system into zones might not be so easy as there is no clear subdivision of per floor plumbing, due to the drops to the first floor and lower floor. It is something I'd consider in time when I replace this boiler, but it would be fairly disruptive trying to discover the CH plumbing layout. (Though I have discovered some of the main runs and with further renovation in the house, I should be able to find the remainder!)

I do have an Evohome setup for controlling the system (that I've installed as part of the overhaul) so that is providing me with pseudo zoning in any case. Simon
 
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I'll double check at the weekend, but i'm pretty sure it's cutting out before the return gets hot, but the flow gets hot as expected. Eventually, the return will get warm, but that's before all the radiators are getting hot. I've tried so many things, I'll try and be a little more structured and methodical to figure out what's wrong.

Appreciate it might not be ideal for the size of house, but it's what we inherited when we bought it, and with TRVs and the rough balancing I described above, it works reasonably well. It just seemed abnormal to me to have to close down the lockshield valves so far on some rads. Also I wondered if pumps degrade with time - ie, it's definitely working, but I'm not sure if it's working as well as a new one, but ideally, don't want to leap to chasing problems by switching out components one by one if I can help it.

Splitting the system into zones might not be so easy as there is no clear subdivision of per floor plumbing, due to the drops to the first floor and lower floor. It is something I'd consider in time when I replace this boiler, but it would be fairly disruptive trying to discover the CH plumbing layout. (Though I have discovered some of the main runs and with further renovation in the house, I should be able to find the remainder!)

I do have an Evohome setup for controlling the system (that I've installed as part of the overhaul) so that is providing me with pseudo zoning in any case. Simon

The return pipe should be getting hot. If it isn't it sounds like the pump
isn't getting the heat away from the boiler.
 
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