Heating system circulation problem
- Thread starter pat1mac
- Start date
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Tiny bit of black sediment at start but clean water mostly. The water flow rate was very erratic though, less so when I reversed the flow, but still doesnt seem to be as strong as the mains input flow.
Softus
I've just checked this and find I have 4 posts, one which is locked and cannot be used and this current one. In my work, Project management, I have to double everything to bring projects in on cost and time, I didn't think plumbers did the same !.
Seriously, I appreciate your advice. I've just checked the flow rate from one rad after disconnecting and using a hose from the valve into a bucket. It seems quite strong, but doesn't seem to obviously change if the pump is switched on and off. I would expect the volume of water ( How do you know if the correct volume of water is moving round the heating system ?) would be similar to a garden pump. Also how can you check the return flow rate, since when you attach a hose to the return valve it will flow in the opposite direction, (into the bucket).
Sorry if I sound dim on this, but there is little information on how heating systems work, apart from this forum.
I've just checked this and find I have 4 posts, one which is locked and cannot be used and this current one. In my work, Project management, I have to double everything to bring projects in on cost and time, I didn't think plumbers did the same !.
Seriously, I appreciate your advice. I've just checked the flow rate from one rad after disconnecting and using a hose from the valve into a bucket. It seems quite strong, but doesn't seem to obviously change if the pump is switched on and off. I would expect the volume of water ( How do you know if the correct volume of water is moving round the heating system ?) would be similar to a garden pump. Also how can you check the return flow rate, since when you attach a hose to the return valve it will flow in the opposite direction, (into the bucket).
Sorry if I sound dim on this, but there is little information on how heating systems work, apart from this forum.
I bet your boiler's full of rust/scale.
Don't know the viscera of this one but some had spreader tubes inside, on the return, like a pipe with holes in, which of course block up. Call to Ideal (ask for Dave Kemp if you get a wombat) should enlighten.
AT the front of the boiler, at the bottom, there's probably a drain cock in a 2" cast iron bung, If you take that (both) out, you should be ableto scrape piles of rubbish out, with a flat strip of metal about 1/2" wide.
Don't know the viscera of this one but some had spreader tubes inside, on the return, like a pipe with holes in, which of course block up. Call to Ideal (ask for Dave Kemp if you get a wombat) should enlighten.
AT the front of the boiler, at the bottom, there's probably a drain cock in a 2" cast iron bung, If you take that (both) out, you should be ableto scrape piles of rubbish out, with a flat strip of metal about 1/2" wide.
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The volume of water will depend on the total water capacity of the boiler plus pipes plus radiators. It's not the volume that matters but the rate at which the water is circulated. This is calculated from the following formula:
Q= P/(4.12 X T)
where
Q is the flow in litres per second
P is the power output of boiler in kW
4.12 is the specific heat capacity of water
T is the temperature difference between water leaving and entering the boiler
Assuming the usual 11°C temperature drop, your 41.9kW boiler will require a flow rate of 41.9/(4.2 x 11) = 0.91 litres per second. As I said earlier this is at the upper limit of the capabilities of the 15-60 and 15-25 pumps. It would only be able to deliver this rate against a head less than 1.25 metres
The whole installation can be considered as a closed system, so the flow rate of water leaving the boiler must be the same as the water returning to
the boiler.
You say you have a thermometer near the pump. If it is the type which clips on the pipe, take it off and attach it to the flow pipe out of the boiler and check the temperature. Then put it on the return and check the temperature. There should not be more than about 11°C difference between flow and return. You say that the return pipes are cold so possibly the temperature difference is more than 11°C.
If there was a blockage in the return to the boiler, there would be no flow so the boiler would overheat and cut out.
Of course, whatever the temperature difference, it is due to the heat being lost in the pipes and radiators. The trick is to get the heat distributed through out the radiators; this is called balancing.
There are only 12 rads, and it's a 40kW boiler. They'd have to be enormous to not get hot without difficulty, unless the balancing is hopeless.
Shut all the rads, open them just half a turn then you know they should all get reasonable flow.
At about 1-2 turns turn open, arad valve is effectively open full, and can short-circuit the flow back to the boiler if it's opened much more than that.
Your flushing helped so you know you had a sludge problem. X400 needs to be left several weeks to wrok well, and it's about the gentlest chemical you can get, so you would expect anytning heavy to still be in there.
I recently tried dissloving heat exchanger scale - nothing did it convincingly, including hydrochloric acid.
Shut all the rads, open them just half a turn then you know they should all get reasonable flow.
At about 1-2 turns turn open, arad valve is effectively open full, and can short-circuit the flow back to the boiler if it's opened much more than that.
Your flushing helped so you know you had a sludge problem. X400 needs to be left several weeks to wrok well, and it's about the gentlest chemical you can get, so you would expect anytning heavy to still be in there.
I recently tried dissloving heat exchanger scale - nothing did it convincingly, including hydrochloric acid.
Hi Guys,
The heating system has improved dramatically, apart from 1 rad now, every rad is hot though I've done nothing. The F&E tank is full and there is no underground heater pipes but thanks for idea anyway. The boiler thermometer is fixed into the 28 mm pipework before the pump, but there is a second scale on this meter in units of mWS, scale from 0-10, this currently shows 4. I presume its pressure or flow but I have no idea what the units are. The temperature is now 80C out but only lukewarm to touch on return, definitely not 10C difference.
I'll try your ideas on the boiler ChrisR and balancing D-Halisham. Thanks again for all you feedback.
The heating system has improved dramatically, apart from 1 rad now, every rad is hot though I've done nothing. The F&E tank is full and there is no underground heater pipes but thanks for idea anyway. The boiler thermometer is fixed into the 28 mm pipework before the pump, but there is a second scale on this meter in units of mWS, scale from 0-10, this currently shows 4. I presume its pressure or flow but I have no idea what the units are. The temperature is now 80C out but only lukewarm to touch on return, definitely not 10C difference.
I'll try your ideas on the boiler ChrisR and balancing D-Halisham. Thanks again for all you feedback.
The other dial is probably measuring the head, though I would expect the units to be shown as mWG (meters, water gauge).
What happens to the reading if you change the pump setting?
If the reading is the head, it is way beyond the capabilities of your pump. A Grundfos 15-60, or 25-60 can only deliver 0.91litre/second if the head is less than 1.25 metres. If the head is 4 metres, the flow rate will only be about 0.36 litres/second. This will mean a temperature drop of about 28°C, i.e. flow 80°C and return 52°C. The boiler will have to work overtime to maintain this differential, so the fuel consumption will go up.
D-Halisham wrote
Definitely in mWS, changed pump speed no effect but when there was air in the system the reading dropped every time air passed through.
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