Heating system circulation problem

[pat1mac]

Hi Guys
I'm at my wits end in trying to sort out my heating system.
Its a very old Oil boiler (Ideal Falcon 2 for whats it worth ), housed in a shed near the house, feeding about 12 rads (cylinder is fed currently from a solid fuel stove). Upstairs rads get pretty hot, downstairs warmish but some cold.
The only major problem I can see is that all of the return feeds from the rads, plus the return 28mm pipe all seem cold though the inlet pipe from the boiler and the feeds to the rads seem hot in most cases. There is also some whooshing noise through the pump (Kettling ?), but its always been like that.
I've flushed the system out with Sentinel X400 (4weeks in the system then flushed out). Not much improvement. Went and balanced all the rads still no major improvement. I thought it might be the pump not able to cope with the long run from the outside shed so I've upgraded the pump from a Grundfos 15-60 to a 25 -60 180, still no improvement.
Is it normal for the return pipe work to be cold ?, maybe I have a blockage or something. I would really appreciate any ideas from anyone out there ?

 

[Softus]

Hi Guys
I'm at my wits end in trying to sort out my heating system.
Its a very old Oil boiler (Ideal Falcon 2 for whats it worth ), housed in a shed near the house, feeding about 12 rads (cylinder is fed currently from a solid fuel stove). Upstairs rads get pretty hot, downstairs warmish but some cold.

Out of balance, or weak pump, or boiler heat output severely reduced.

The only major problem I can see is that all of the return feeds from the rads, plus the return 28mm pipe all seem cold though the inlet pipe from the boiler and the feeds to the rads seem hot in most cases.

With a major problem like that, you only need one.

There is also some whooshing noise through the pump (Kettling ?), but its always been like that.

Isn't it odd that the noise has stayed even though you've replaced the pump?

Have you vented the pump?

 

[pat1mac]

Thanks for reply Softus. Yes, I've bled the pump after replacing. I thought this pump ( 25-60) would be more powerful than the 15-60 that it replaced. Its on highest setting (3). Its probably the boiler. Its over 20 years old. The temp gauge on the pump boiler side shows about 70C when the boiler is heating. Is this the normal output ? I can turn the boiler up but I'm worried that the kettling will get worse. The bypass pipe return gets hot ( presumably its supposed to do this) but the heating return is cold. I'll try and balance the system again. Thanks for your help anyway.

 

[JohnD]

.... The bypass pipe return gets hot ...

Aha!

Does it have a gate valve to adjust the amount of bypass flow?

 

[Softus]

I thought this pump ( 25-60) would be more powerful than the 15-60 that it replaced.

I don't know why you thought that.

Its on highest setting (3).

Oh.

Its probably the boiler.

You have the march on me there. Why do you think it's the boiler?

Its over 20 years old. The temp gauge on the pump boiler side shows about 70C when the boiler is heating. Is this the normal output ?

It's a bit low, but it's related to the return temperature, and you've got a new pump running at top whack.

I can turn the boiler up but I'm worried that the kettling will get worse.

At what position is the temperature control?

The bypass pipe return gets hot ( presumably its supposed to do this) but the heating return is cold. I'll try and balance the system again.

Please see JohnD's comment/question.

 

[pat1mac]

Thanks guys for interest,
The heating engineer that serviced the boiler last year came out yesterday and shut off the jammed Bypass valve. ( JohnD's query) He could not sort the circulation problem out, said the boiler was old and needed replacing. (He said that last year as well, thats why I thought the boiler was the fault). In fact after he left things have deteriorated even more. I now have just 2 rads hot nearest the boiler, and 2 lukewarm, rest cold. Previous to his visit, most of upstairs was hot
The boiler is set to about 70C on its thermostat. Temperature gauge near the pump shows 75C. I can see and feel the pump operating. I can get access to the 28mm heating pipework nearest the hot rads (towards the other rads), and its hot on the feed side and cold on the return. The boiler switches off most of the time as well (temp is reached presumably)., but most rads are still cold. I've tried turning up boiler temp to 85C but no change to other rads. Pump and rads have also been vented.
I tried flushing through with mains water into the boiler draincock and out on furthest rad draincock, and clean water comes out. (Pump valve closed). This I suppose checks the return pipework. I've even changed the pump back to the 15-60 pump. Nothing seems to make a difference. I've also tried shutting off the 2 hot rads but the other rads don't change in temp. I can only presume that hot water from the boiler is unable to flow to the cold rads due to an airlock or blockage somewhere. Any further ideas guys on narrowing things down. ?

 

[tryitandsee]

Thinking out loud!

When you changed the pumps (twice in your case), make sure the gates are opening fully in the pump isolating valves. Sometimes the spindles are turning but the gate is not lifting fully.

 

[pat1mac]

Thanks Tryitandsee, I might try and reverse the pump ( was that JohnD's idea to try and clear airlocks ?)'and check gates same time.
By the way didn't get a chance to thank you JohnD for you suggestion with a previous problem on controlling cylinder flow to help improve rad heating. I put a 2 way valve in and it all worked a treat. In fact thats the only time all rads were all hot in the last 3 years. It lasted 2 weeks, then for some reason I decided to clean the wiring up (why oh why didn't I quit when I was winning ). I tried to upgrade the wiring so that the room stat would control the boiler and pump from the Programmer. The pump was running all time heating is on, no room stat control for boiler etc, (very old system) when due to some cockup (probably my wiring), the boiler stat did not operate and the boiler heated to 100C before I could switch it off and restore wiring back to old style set up.
Can't understand why the heating went back to its old ways after that, of hot rads upstairs, few cooler rads downstairs.

 

[Softus]

To recap....

The radiators are colder than you would expect.

Closing the bypass valve has made this symptom worse.

The temperature of the water reaching the pump, which is distant from the boiler, is what you would expect it to be.

The return to the boiler is colder than you would expect.

The relative layout of your vent, cold feed and pump is unknown.
____________________________

Could you expand on your description of your entire system?

Photos of the pipework layout near your pump, and near the hot water cylinder, would be useful.

Could you report on the state of the contents of your F&E cistern? Colour, water level, odour, general gloopiness, etc..

 

[wilhelm]

Is the boiler underfired? Them falcons are big boilers.

 

[pat1mac]

Hi Guys,
Status so far: Only 2 rads now hot ( both nearest to boiler). Rest cold Boiler temp 75C at pump. Pump seems to be running ok.

Softus,

pics can be found if you search under my name

Pat1mac

, see link below.
F&E tank full, cleaned out 3 months ago month prior to adding Sentinal X400 for a month. Its been drained several times since for various reasons ( see saga above and previous.). Any subsequent draining of system shows clean water. The boiler is 41.9kW, the service engineer said it was more than capable of driving 12 medium size double rads.
The boiler is in a shed near the house, with pump ajacent. F&E tank in loft. 28mm pipes feed from the boiler under the floor of the 1st floor. Ground floor rads are fed from this 1st floor. Both hot rads are nearest boiler on ground and 1st floor. The cylinder is now isolated and fed from a solid fuel range. At least thats hot. Only temp control for boiler is the boiler stat. Boiler and pump switch on by the programmer timer. Very old and simple system. No Motorised valves etc.

Rads hot upstairs, cold downstairs : unfolding saga
Thanks JohnD for web link to photos Photos as follows:

pat1mac | Plumbing and Central Heating | www.diynot.com/forums/viewtopic.php?p=841551#841551 - 29 February 2008 2:21 pm

 

[Softus]

Having just this moment discovered that you've created about six topics covering the very same problem, I've almost lost the will to live, but am struggling through to offer the following advice...

Just because you have clear water coming out doesn't mean that there isn't debris in the system. If all that's left is 20 years old and caked on, then it won't easily come out.

I reckon that you have at least one blockage. This/these could be in:

1. Boiler HEX;
2. Pipework;
3. Many rads;
4. Many TRVs.

If it's the boiler then you have the option of replacing the HEX or the entire boiler, but you wouldn't want to do that without ridding the rest of the system of debris.

It was unwise to install TRVs on a dirty system - they don't behave well with crud inside them.

If I were there I would pick on a cold rad, shut off its valves, remove it, then empty and remove the rad. Couple up a length of hose to each rad valve in turn, and, with the pump running but not necessarily with the boiler burning), open the valve and run the hose it into a bucket to test the Flow and Return flow rate.

Do this with as many rads as you like, depending on what you discover, and you'll have a map of how well the water is circulating around the system.

You'll also discover whether you have any blocked or stuck-shut TRVs.

One more tip/request: don't create any more topics for this problem until it's solved.

 

[D_Hailsham]

The boiler is 41.9kW, the service engineer said it was more than capable of driving 12 medium size double rads.

That's a very big boiler for the average sized house.

If the boiler is running set to max output and assuming the usual a temp drop of 11°C between flow and return, the water flow rate would be 41.9/(4.2 X 11) litres per second i.e 0.91 litres per second. This is at the very upper end of the performance of the 15-60 and 25-60 pumps. (The performance of these pumps is identical. The only difference is that one has a 15mm bore and the other a 25mm bore; the head in both cases is 6 metres.)

Without knowing more about your system it's not possible to calculate the correct sized pump. You need to get that right first.

You need to work out the total heat output of you radiators. Assuming the radiators are all the flat steel panel type, you can use the Stelrad Elite information to get a close approximation.

The other thing needed is the length of the pipe run (flow + return) from boiler to the furthest radiator. From this the pump head can be estimated.

 

[foley74]

Are you sure the system is full or its not pumping over,so when your venting is the h/tank filling up.I would first off get a valve to shut the h/w circs off,and then see how it is,if theres water in the system and its firing up,pump working then the heat iss obviuosly going somewere and if the rads arent hot then the circs must be robbing it,see the older the systems get the more they start needing more balancing and looking after

 

[pat1mac]

Guys, Thanks for your ideas.
Softus - sorry about confusion , but I've had several problems with the heating system over the last 6 months and wasn't sure how to reopen old topics.
Today I used mains water to flush out the pipework from the boiler output to the furthest rad input. The drained water was still restricted somewhere ( I also tried reversing the water flow) but there has been some improvement since I now have most of the upstairs rads hot again, and 2 rads downstairs with heat. There are still 3/4 rads, mostly downstairs cold, it looks like there is still some obstruction in the pipework. The whooshing noise has gone after replacing and closing the bypass valve.

I'll take onboard your advice on trying to narrow down the rad obstruction from here. Thanks for your patience guys.