Rads still cold on ground floor in 3 storey house.

[Marky]

Hi

Maybe someone can advise on this scenario:

Property: 3 storey semi-detached townhouse, built c.2004.
Hot water: Megaflow system, in upstairs airing cupboard, which works well.
Heating plumbing: 10mm plastic microbore, header tank in the loft.
Boiler: Natural gas IDEAL Logic 18Kw+ (upgraded from 15Kw) - ground floor.

Completed in the last 24 months:
New upgraded boiler, new upgraded pump, 2 new motorised valves, new controller, cleaning additive, 2 power flushes, boiler 1st service, inhibitor, system balanced and several rads removed and flushed with a hose. The guys who fitted the boiler and did the power flushing and balancing seemed good and came back 3 times.

Problem:
Some cold or only slightly warm rads on the ground floor.

If I attach a hose to the drain cock of any of these rads and drain outside, I can get the rads hot, but as soon as I stop, they cool down again, even with the rads on the top floor shut off.

There is very hot CH water reaching the ground floor, but it is not going through all the rads. I have bled all rads as well as the pump.

I have spent many hours on this, and several plumbers and heating engineers have too. There are no leaks. When water is drained off through the drain cocks of the downstairs rads, the water does sometimes seem slightly aerated with bubbles.

One heating engineer suggested raising the loft header tank on a platform (there is not much room, but it could go up about 3 foot). The overflow into this tank does run a lot.

I suppose there is a manifold for the microbore system? If so, it was buried under floorboards somewhere by the builders and both they and the previous owners of the house, are not helpful.

I would be very grateful for any advice. I have spent getting on for £3,000 getting my heating right, and I still have cold rads.

Thank you.

 

[Riley]

Very difficult to speculate could be blocked mirobore, kinked microbore, poorly designed system pump in wrong place. Too long pipe runs or pipes poorly sized. I’d be tempted to seal the system.

 

[dancinplumba]

blockage on 10mm plastic, rip out and redo, flush means nothing to be honest

 

[SimonG]

Its a flow issue or more to the point a lack of flow.

Rileys covered all the bases.

Needs a right good look by somebody who knows what they are doing.

 

[king of pipes]

Agree with Riley seal the system. Kop

 

[Jones82]

Undersized pipework, the 10mm is running too far to radiators that are too big.

Find the pipe runs to the downstairs radiators and upgrade as much as possible to 15mm.

Unfortunately this may mean replacing the 10mm drops buried in the walls.

I bet the pump is on the top floor?

When they originally installed your system they used a 22-10mm manifold, then ran 10mm to the radiators, the position of this manifold is too far away from the ground floor radiators. Seen it loads on new builds.

 

[townfanjon]

Have you been in the house from new , was it right in the first place ?

 

[doitmyself]

One heating engineer suggested raising the loft header tank on a platform (there is not much room, but it could go up about 3 foot). The overflow into this tank does run a lot.

1. Is the pump on the top floor?
2. If so, what is the vertical distance between the pump and the header tank?
3. Which pump do you have and what speed setting is it on?
4. How deep is the water in the header tank when it is cold?

The "overflow" is, I assume, the pipe which goes up past the tank and loops over to empty into the tank. If so, it sounds as if the top of the loop is not high enough above the water level. It should be 450mm minimum. Incidentally, this is a vent pipe, not an overflow.

 

[Marky]

Thanks for all replies.

The pump is in the airing cupboard and the header tank about 8' above it in the loft. The pump is on medium speed setting. The top of the loop of the vent pipe is about 8" above the water level in the header tank, which is always 3/4 full.

After draining a lot of aerated, bubbly water out of the system last night, I have got the downstairs rads a bit warmer.

I think it is a poorly designed system. Luckily the house is well insulated so it is not too cold. I am thinking that it is worth first raising the header tank and vent pipe, as suggested, and seeing if that improves matters. If not, then a sealed, pressurised system is on the cards.

 

[doitmyself]

The pump is in the airing cupboard and the header tank about 8' above it in the loft.

There is no need to raise the tank any higher as 8ft will provide more than sufficient static head at the pump inlet.

The top of the loop of the vent pipe is about 8" above the water level in the header tank, which is always 3/4 full.

That's where the problem lies.

1. The tank is too full. The float valve needs be adjusted so it will be open when the level is about 2" above the cold feed exit. The actual cold level will be higher than this when the valve shuts off.

2. The vent pipe will need extending if the top of the loop is not 450mm above the cold water level.

 

[Marky]

Many thanks <doityourself>.


I have lowered the water level in the expansion tank in the loft by bending the arm of the ball valve.


The rads on the ground floor are a bit better, but there is still a flow of hot water from the vent pipe, even with the pump on the lowest speed setting. The expansion tank is basically acting like a radiator – I am sure that the spider community in the loft is most grateful!


So this week I am arranging to have the top of the loop of the vent pipe raised. In fact, the current vent pipe does not have a loop, it is a right angle.


I am guessing that this continual running of hot water from the vent pipe when the CH is on is the cause of the air in the system.


Best.

 

[Frog67]

You say hot water is reaching the ground floor rads but the rads are at best only warm?
This to me sounds like a restriction in the return pipework probably in the manifold.
I would be looking to locate the manifold supplying the cool rads.
Turn off all rads except the ground floor ones and note if the boiler runs or shuts down on its thermostat
If the boiler shuts down quickly then this would suggest a blockage
You could try adding some strong cleaner X800 or MC5 and try to turn off as many rads other than the ground floor ones without the boiler shutting down. This may clear any restrictions and could stop the over pumping in the loft