all radiators warm, not hot. except yesterday!

[paffel]

Hi all, looking for some guidance.

A simple heating system. potterton suprima boiler, gravity fed feed and expansion, around 18 years old. Its powering a 3 bed detached, hot water done by immersion only.

have set boiler stat just short of max, and room stat at 25, but house rarely get above 18.

all radiators are warm but not hot. All were bled the other day and one had about half air in it, other than that all were fine.

Yesterday evening, after turning programmer off for an hour, then firing it up again, all rads became hot, too hot to touch - it raised house temperature lovely!

But today, back to warm only!
The boiler flashes green to indicate that its reached temperature, but the flow and return pipes from the boiler are warm only, not hot.

Any ideas?

 

[JohnD]

poor circulation, could be worn out pump, very likely sludge and sediment. Does the pump feel hotter than the pipes going into it?

you say the flow pipe from the boiler is not hot, so it doesn't sound like a bypass (unless it is before the pipe you felt). It could possibly be the boiler stat. When was the boiler last serviced? Has the system ever been cleaned? Can you do simple plumbing?

Are the radiators warmer at the sides and top than in the middle?

it is very strange to have a gas boiler and a hot water cylinder where the boiler does not heat the cylinder. Do you know why it was done like that? Energy from electricity costs about three times as much as energy from gas, so you are wasting about 50p every day of the year.

 

[paffel]

Appreciate the reply.

the pump body is definitely hotter than the the connected pipes, but I wouldn't call it extremely hot. It does gurgle when on, I've assumed air is in the system. Its a grundfos, but the bleed screw is not very accessible due to the pumps vicinity to the HWC.

Boiler last services 6 months ago, just before I moved in, report showed everything healthy. I've not noticed a deterioration in the systems effectiveness but we've had a cold few Weeks and the problem may just be revealing itself now.

The radiator temperature feels fairly consistent, although a couple are slightly cooler towards the bottom in the middle.

The setup is strange, I agree, its an old east midlands thing, my elec is economy 10, so I guessed they intended to fit storage heaters initially on build of the house (97 I think) but for some reason installed a gas central heating system!

The difference between last nights radiator temp and tonights is significant - for the rest of last week the temperature was also just warm, never hot.

 

[paffel]

Also, I'm not sure about the systems history, whether inhibitors or descalers have ever been added - I'm not much of a plumber but I'm pretty sure I could isolate and remove a rad, that's probably my limit if that gives you an indication!

 

[JohnD]

if the pump is hotter than the pipes, it is not circulating water properly. It might be seized, or worn out, or clogged with sediment. Do your best to open the bleed screw and see if water drips out, and if you can turn the motor spindle with a screwdriver in the slot.

Post a pic of the pipe layout around the cylinder and pump. It is possible to remove a pump but the pump valves might be seized.

When you bleed the radiators, is there much gas, and what colour is the water?

Bleed the highest radiator ion the house and see if water squirts out forcefully.

Look for the system drain cock, which might be near the boiler, or by a downstairs radiator near an external door. It will have a squared shaft, and a spigot that a hosepipe would fit. It never hurts to give a simple chemical clean to an old, open-vented system, and is likely to do some good.

 

[jeff the gasman]

If all the radiators get warm evenly and both pipes to each radiator are warm, I wouldn't be thinking circulation.
I would be checking for a faulty flow thermistor on the boiler.
Jeff.

 

[paffel]

ILast night it became hot too, but for the majority of the day it was warm.
Today, much of the same - just warm.

all radiators are very close to each other in terms of output, there's not one radiator that I'd consider to be better/worse than the others.

If the thermistor is playing up, I'm hoping the part is still available? Guessing it might be worth testing it with a multimeter anyway?

pictures of the pump.

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• paffel
• 25 Jan 2015
• 1

Bottom half of the pipework in the cupboard;

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• paffel
• 25 Jan 2015
• 1

Top half;

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• paffel
• 25 Jan 2015
• 1

And this demonstrates the clearance i have for the front of the pump - I've got an adjustable spanner with a 1p in it - It will go in the screw but I'm obstructed when turning it by the cylinder or pipework!

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• paffel
• 25 Jan 2015
• 1

 

[paffel]

Have also just turned system off and bled an upstairs radiator. Water comes out, out looks surprisingly clear, but there's a definite hint of black in it.

 

[JohnD]

is the pump still hotter than the pipes that go into it?

 

[paffel]

It sure is. The pipes are warm to the touch, estimate somewhere around 35 deg C. the pump body is hot, but you can still hold it. Perhaps somewhere around 50, just to give an idea.

I've some a lot of reading about the Suprima, they are prone to electrical failures. Our boiler looks to have had a new PCB at some point, as it's been fitted with a newer Siemens one, rather than the old Enertech one.

Apparently these newer PCBs present problems on failure too - same symptoms as mine (runs for 3 minutes, then reports temperature satisfied, repeat; warm but not hot rads, warm but not hot flow pipe).

My current thoughts are to run a multi across the thermistor, and see if it's within tolerance. If the PCB needs replacing, its £170, not horrific in the grand scheme, but I'd rather spend a tenner on a new thermistor first if I thought that was the cause.

 

[JohnD]

regardless of the boiler thermistor, a hot pump still indicates poor circulation. You can turn off the pump valves (they will probably leak) and remove the pump for a look.

 

[paffel]

Tonight we're back to hot all over., pump is about as hot as the pipes, I can't keep my hands on either for long.

The pump is gurgling still, there also might be a rattle inside it too, so it definitely needs investigating.

 

[jeff the gasman]

If it's gurgling and rattling, don't waste your money on a thermistor.
Jeff

 

[Dan Robinson]

a hot pump still indicates poor circulation.

No it doesn't

 

[paffel]

Just an update for this;

A common problem with these is dry joints on the PCB. On removal, it was apparent there were 4 dry joints for 2 relays.
A quick resolder and all sorted - I now have heat - and have done consistently for about 36 hours now.

Here's a picture of the PCB, the dry joints are near resistor 418.

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• paffel
• 1 Feb 2015
• 1

Thanks to all for your inputs - the pump does need to be investigated as it is noisy but at least for now the house is warm.