I just measured the power consumption of the original circulation pump that was retained when the GSHP was fitted. It is consuming 85 watts.
CH Circulation pump (?) fault diagnosis
- Thread starter Just4Fun
- Start date
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How many rads on the system exactly ? Do they all get hot in normal use? Do you have cold spots on any of them ? This can be checked by feeling the top and bottom of the rads. If the tops are hot but the bottom warm or worse cold this is a good indicator of sludge within the rads . Copper pipe work can also be checked with a decent magnet as if it attracts to the copper pipe this will be sludge solidified within the copper pipes. This could be what is now causing the issue and would certainly explain why it’s intermittent. If you have an above average amount of rads the extra pump could have been fitted to increase the circulation.
I haven't counted the rads exactly. I would guess about 45.
Not all of the rads are turned on. All the rads that are turned on do get "hot" I think, but "hot" is a relative term. The water flows at a temperature of 40C to 44C in the current conditions, and never gets above 55C even in cold weather, so the rads are not as hot as a typical UK system. I haven't noticed any rads with cold spots. The pipework is iron, not copper, so the magnet trick won't help and anyway the only pipework that is visible is the vertical risers at each rad. Most of the pipework is below the floorboards. When I bleed the rads the water comes out fairly clean; I have seen systems that are much worse.
I have currently stopped the pump that is a holdover from the pre GSHP days. I'll give it a couple of days to see if/how that affects system performance, and also see if it has an impact on the intermittent problem.
Not all of the rads are turned on. All the rads that are turned on do get "hot" I think, but "hot" is a relative term. The water flows at a temperature of 40C to 44C in the current conditions, and never gets above 55C even in cold weather, so the rads are not as hot as a typical UK system. I haven't noticed any rads with cold spots. The pipework is iron, not copper, so the magnet trick won't help and anyway the only pipework that is visible is the vertical risers at each rad. Most of the pipework is below the floorboards. When I bleed the rads the water comes out fairly clean; I have seen systems that are much worse.
I have currently stopped the pump that is a holdover from the pre GSHP days. I'll give it a couple of days to see if/how that affects system performance, and also see if it has an impact on the intermittent problem.
I think the end result is probably like any communication network in that it will default to the speed of the slowest device. These pumps are not positive displacement, just circulators and unless they are both trying to move the same flow of water then one must restrict the flow. If both were identical then they must be additive but not sure if this applies to circulators.
nolly47
Established Member
Hi
I don’t know a lot about finish central heating systems
So, the ground source heat pump I assume is on 24/7 and controls the house temp with its weather compensator?
The radiator pump runs the central heating water for the radiator and has no controls on it and runs 24/7 I assume this is a leftover from the oil central heating?
When the fault occurs how long does it last for and how does it right itself?
Does the same water run through the ground source heat pump and central heating system or is there a heat exchanger fitted to separate them?
I don’t know a lot about finish central heating systems
So, the ground source heat pump I assume is on 24/7 and controls the house temp with its weather compensator?
The radiator pump runs the central heating water for the radiator and has no controls on it and runs 24/7 I assume this is a leftover from the oil central heating?
When the fault occurs how long does it last for and how does it right itself?
Does the same water run through the ground source heat pump and central heating system or is there a heat exchanger fitted to separate them?
Yes, exactly so.
Yes. This is an old pump that is in series with another pump that is part of the GSHP. The old pump runs 24/7 and the pump in the GSHP is controlled by the GSHP.
When the fault occurs the system does not reset itself, so the fault condition persists until I do something to get things working again.
There are 2 water circuits. One contains water with an antifreeze additive and runs through pipes buried in the field at the back of the house. The other runs through the radiators. Both loops run through the GSHP with no direct connection between the 2 loops. Instead, the GSHP acts like a fridge in reverse, taking energy out of the field loop and putting it into the radiator loop. So a bit more complicated than a simple heat exchanger, but similar in principle I guess.
Myfordman
AKA 9Fingers
The capacitor in a pump is a run capacitor and is needed for for both start and run.
Ok Just for fun you are really Dick Strawbridge and I claim my £5 . 45 rads must be a chateaux you live in 
OK, so that knocks my theory on the head.
Ok Just for fun you are really Dick Strawbridge and I claim my £5 . 45 rads must be a chateaux you live in
No £5 for you I'm afraid, but yes, it is a big old house. Count the windows: most of them have a rad below them.Attachments
Lons
Established Member
The screwdriver on the pump with the handle to your ear certainly confirms the shaft is spinning but far from foolproof as I found out a couple of years ago when after replacing the pump as a last resort I found the impeller had sheared off the shaft of the original. I couldn't understand why the pump was spinning but pipe was cold until I dismantled the old one.
Old.bodger
Established Member
I have skip read this so please excuse if I have missed a vital fact!
is it possible that one pump is circulating the glycol mixture in the heat pump and the other the water around the heating system. I would expect a buffer tank between the two.
This would certainly explain the two pumps.
is it possible that one pump is circulating the glycol mixture in the heat pump and the other the water around the heating system. I would expect a buffer tank between the two.
This would certainly explain the two pumps.
Richard_C
Established Member
That seems very likely to me. I can't see how else you can keep the glycol and the radiator water separate with just one pump, unless you have one pump motor with 2 impellers/circulators, (I've never seen one but maybe they exist.) Both need to run to keep the rads warm but they may be doing diferent things.
Is that which leaks out of the pump water or glycol, and what about the other pump?
My goodness its the Von Trapp school of music, Nice pile you have thereOK, so that knocks my theory on the head.
1steven
Claremorris Ireland
These are handy for testing circulating pumps.
That gizmo only tell you that the motor shaft is turning. It does not tell you whether the impeller has become detached from the motor shaft.
1steven
Claremorris Ireland
In forty years as a heating engineer never had a Grundfos let go of the impeller. Maybe I was lucky
mostly happened on Wilo ones.Had a couple of Grundfos let go but, as you say, the Wilos are known for it.In forty years as a heating engineer never had a Grundfos let go of the impeller. Maybe I was lucky
pe2dave
Established Member
You did say it was 'rather complex' to fully describe!
I agree.
I agree.
1steven
Claremorris Ireland
First couple of Wilos caught me out after that first thing to check was the impeller
