C.H. System Inefficient

[Biddulphian]

My house was built around 1979 and has a central heating system with microbore pipe work, 5 rads upstairs & 4 downstairs. We changed the original boiler and open system to a Baxi Duotec HE 28 condensing combi boiler a number of years ago when we moved here. We are struggling to heat the house fully, as in the rads don't get hot enough. The heating engineer who services the boiler for me once a year has told me that the boiler is fine and the problem is due to the microbore pipes. The boiler short cycles when the heating is on. Over the last couple of years I have had the most problematic rads off and given them a good flushing outside, I have run Sentinel X400 through the system and then flushed the system and each rad individually using the filling loop and system drain cock, then topped up and added X100 inhibitor. If I isolate all the rads except one, that one open rad will get plenty hot enough, so I know each rad and it's pipework works fine, but with all rads open they get warm but not very hot. I have done a general balancing to prevent the upstairs rads getting preference on the heat so they all warm up, but don't get hot enough. The engineer who does my service said he did not recommend a powerflush on the system as it might cause further problems and the system maybe clean enough now to not warrant it anyway.
Has anybody got any other tips or advice for me to try to get warm?
Thanks for reading.

 

[Old Salt]

Get rid of the micro bore pipework. I have had 2 houses with micro bore and both gave problems.

 

[Biddulphian]

Get rid of the micro bore pipework. I have had 2 houses with micro bore and both gave problems.

That's the nuclear option I'm hoping to avoid as it would involve major disruption in the house.
Would a powerflush really not be worth it do you think?
And what about removing a rad and connecting a hose up from a tap to the rad valve and another to drain and trying a mains powered flush that way, would that be worth a try?

 

[fixitflav]

My house was built around 1979 and has a central heating system with microbore pipe work, 5 rads upstairs & 4 downstairs. We changed the original boiler and open system to a Baxi Duotec HE 28 condensing combi boiler a number of years ago when we moved here. We are struggling to heat the house fully, as in the rads don't get hot enough. The heating engineer who services the boiler for me once a year has told me that the boiler is fine and the problem is due to the microbore pipes. The boiler short cycles when the heating is on. Over the last couple of years I have had the most problematic rads off and given them a good flushing outside, I have run Sentinel X400 through the system and then flushed the system and each rad individually using the filling loop and system drain cock, then topped up and added X100 inhibitor. If I isolate all the rads except one, that one open rad will get plenty hot enough, so I know each rad and it's pipework works fine, but with all rads open they get warm but not very hot. I have done a general balancing to prevent the upstairs rads getting preference on the heat so they all warm up, but don't get hot enough. The engineer who does my service said he did not recommend a powerflush on the system as it might cause further problems and the system maybe clean enough now to not warrant it anyway.
Has anybody got any other tips or advice for me to try to get warm?
Thanks for reading.

Is it possible to increase the pump speed? (built-in pump on a combi). If not, maybe worth checking it's not partly blocked with sediment. It doesn't sound like there's a sludge problem in the rest of the system.

 

[Biddulphian]

Is it possible to increase the pump speed? (built-in pump on a combi). If not, maybe worth checking it's not partly blocked with sediment. It doesn't sound like there's a sludge problem in the rest of the system.

One of the things I thought about was pump speed, but it's a fixed speed Grundfos pump so I can't increase it. Would I need to take it out of the boiler to check for sediment?

 

[oldbuffer]

1. Power flushing micro bore is often not successful. You can't get the flow through the pipes, particularly if they are partly blocked.
2. If sludge is the problem, it may well be in the pipework rather than the radiators.
3. You could try a mains flush, but make sure it is directed through all parts of the pipework as well as the radiators.

 

[fixitflav]

One of the things I thought about was pump speed, but it's a fixed speed Grundfos pump so I can't increase it.

This is the pump curve from the manual. I can't see anything about how or why it uses curve I or II, maybe it's for different ratings within the model range. But if you're on I and it can be changed to II it might help. If you haven't got the manual I can attach it.

Would I need to take it out of the boiler to check for sediment?

I wouldn't think so. Motor/impeller held to the pump body by 4 Allen-headed bolts, M5 I think, and look accessible. No need to disturb body or pipework.

 

[fixitflav]

2. If sludge is the problem, it may well be in the pipework rather than the radiators.

He said each rad gets hot if all the others are closed.

 

[martygturner]

Try balancing the flow in the rads along with a heat the system up let cool down and bleed.

see ovo for some help... https://www.ovoenergy.com/guides/energy-guides/how-to-balance-radiators

 

[cross thread]

Filter in the return valve may need cleaning

 

[vulcancontinental]

Filter in the return valve may need cleaning

That's a good call, I don't know whether Baxi's have a filter but a good call if they do. The pump graph shows 5m head at the flow rates the OP is likely to have and if the microbore is manifold fed the resistance will not be that high.

 

[Biddulphian]

Thanks for the replies everybody.
I've had a look at the relevant install/service manual and had a good nose about the actual boiler and I'm fairly sure there is no filter on the return (or flow) pipework to and from the boiler. The pump appears to be running freely too.
I'm tending to think that as the system wasn't looked after before we moved in, there is enough sediment around the system to restrict full flow but the pump can overcome it enough if all but one rad is closed off forcing all flow through just the one. I may get some F3 and run that round for a week or 2 then drain and remove a rad, connect the tails up to a tap via hoses, and spend a day flushing the whole system and individual rads.

 

[cross thread]

On the return isolation tap there is a cap,remove this after draining and you will find a gauze filter .

 

[Biddulphian]

On the return isolation tap there is a cap,remove this after draining and you will find a gauze filter .

Thanks, I'll have a look later after work.

 

[Biddulphian]

On the return isolation tap there is a cap,remove this after draining and you will find a gauze filter .

Just had a quick look before heading out, the filling loop goes into the end of return isolation tap so there is no cap. I presume if I remove the filling loop the filter should be there. Also noticed the flow isolation tap is the same but does have the cap, would there be a filter in there as well?