Open vented microbore CH system problem.

[c572]

I’m hoping that someone on here can help. My partner and I have an open vented CH system, the pipe work is microbore. I’ve drained and refilled the system several times and circulated Fernox but the problem is this...when the heating is on, only some of the radiators are warm at the top and cold in the middle whilst others feel like only a small amount of hot water is getting to them. I replaced an old radiator with a new one and even the new one is only warm at the top. When you turn all the radiators off and I leave the one on the landing (closest to the airing cupboard) its scalding hot all over, the problem starts when I turn on the other radiators. There are 8 radiators in total, though the one in the kitchen is never used. The radiators furthest from the airing cupboard downstairs are the worst for not getting very warm but the ones upstairs in the bedrooms aren’t as bad.

Pump is a grundfos 15-50 and it’s set on speed 2.

I’m considering a power flush for the system but I’m not sure if this will help or make things worse-please can someone advise?

I’ve installed a TF1 omega filter, but I think this may be on the flow rather than return side. Could this be the problem??

There was a gas fired back boiler as the heat source but this was ripped out and has been replaced by a heat exchanger fed from a Solar Bayer stratification system. (The water temperature of the water isn’t the issue, it is scalding).

All of the radiators have lock shield valves on both sides and I know which is glue/return. Do you balance radiators on microbore? If so, how as I’ve not had any experience with microbore systems.

Any help would be gratefully appreciated

 

[Madrab]

Microbore is notoriously difficult. When you say microbore do you mean 8mm pipe? 10mm pipe isn't really microbore, more small bore but nothing in the pics looks smaller than 15mm.

3 possible issues -

1 - Lazy pump
2 - blocked pipework/manifold
3 - system needs properly balanced.

 

[BoredSeb]

That looks like an interesting system! If it is microbore it will be piped differently then a conventional system. Think an 8mm pipe can only carry about 1.5Kw and a 10mm pipe about 2.5Kw.

The flow and returns are usually piped in, say, 22mm to a manifold, and then each rad will have a flow and return from the manifold. Is that how yours is?
It is common for additional rads to be fitted and piped incorrectly!

On a separate note, if you have only recently fitted that filter, It's quite possible that the plate HE is partially blocked - whats the heat transfer like?
Another area for blockages is the neutral point in the system - where the feed connects to the primary, and possibly also on the inlet side of the pump.

HTH

 

[c572]

Hi, the flow and return are indeed 22mm. I'm not certain where the manifold(s) are as I've not ventured to taking up carpet and floorboards yet. The pipe into the pump and from the motorised valve also gets hot when pump is running, as does the inlet/outlet of the coil of the hot water cylinder when it's switched from central heating to hot water. To me this suggests that the heat exchanger is ok. Even when the pump isn't running you can feel the hot water in the flow pipe near the heat exchanger.

I'm wondering if draining the system again would help or if it would be more beneficial to get a powerflush done on the whole system. What are the thoughts on this? I've read about powerflush not being suitable for microbore, but short of ripping up all the carpets and floor boards (something that I don't really want to do unless I have to), I'm at a loss at what else I can do to get the system at least running better than it is at the moment.

 

[c572]

Hi Rob,

It's microbore pipe to all the radiators, I'd say that it is 8mm. The 15/22mm pipe is in the airing cupboard as you already pointed out.

1).When you say 'lazy pump' what do you mean?

2). With regard's block manifolds, would a powerflush make any difference in unblocking them?

3). How do you balance a microbore system?

 

[BoredSeb]

Personally I would initially run Fernox F3 or equivalent cleaner through the system for a week or 2 and then flush and refill.
The only caveat to this is that I would definitely have a filter on the flow to the HE (i.e. the return to your heat source), as it may get blocked (and clean it daily).
Can't comment on the powerflushing.

 

[Madrab]

If you are on 8mm microbore from branch manifolds to the rads then a power flush won't really do much, in fact it can cause other issues as it can force debris into the manifolds making the flow even worse. You also won't get much pressure/flow through the pipe to the rads.

Bottom line and IMHO, the best option, if you want excellent warm up and an efficient system is to replace it ASAP.

You can run an indicative test, drain the worst rads and then crack open each sides valve and see what flow you have through the pipe.

 

[c572]

Thank you for your help so far, I will indeed try the fernox again.
A few other questions I have:

1). As for the balancing side of things, how is this achieved on microbore?
2). If there is adequate water coming from each of the rad valves when I test them to see if their are blocked or not, what would be the next best course of action-flush rads/replace pump??

thanks again for help so far. Back on shifts tomorrow so will update when I get chance to do the suggestions.

 

[Madrab]

If microbore was installed properly then it can be self balancing - centralised manifolds and similar lengths of runs to the rads - unfortunately a lot of installers didn't do this and hence the need for manual balancing.

Balancing on microbore is the same as any other balancing exercise - https://www.diynot.com/wiki/Plumbing:faq2 -

I would check the flow from the valves first and then then look at balancing before looking at the pump. It is typical for old furred up microbore to cause flow issues. I would also pop the pump up to max and see if it improves circulation.

 

[c572]

Update on the situation....

There is adequate flow through both valves at each radiator valve. I have closed all valves and just had the pump serving one radiator downstairs on it speed 2. (It's a grundfos selectric 15-50). The radiator get hot pretty much all over. I've closed that one off and then done the same on another radiator which is also downstairs but further away from the pump and again it get hot pretty much all over. I've repeated this on two radiators upstairs, one next to the airing cupboard an another in one of the bedrooms. Both have the same result.

I did this to prove to myself that the pipework isn't blocked to each radiator. The problems start when I open more than one radiator as initially described. I've tried to increase the pump speed to no.3 and I just get a noisier pump and not much difference in the heat from the radiators.

The pump is at least 15/20 years old. Would changing the pump to a 15-60 i.e. a 6 mtr head improve the situation? Any further advice would be appreciated. Thanks to those for their help so far.

 

[Madrab]

If the pump is that old then it may be getting lazy after all that time pushing against the reduced bore and can't supply enough grunt.

Running a cleaner through the system and then draining and flushing, as was suggested, may help the situation but again it's making sure the system is then flushed clean with the 8mm pipe. If it doesn't then its back to the start.

Also if the 8mm is restricted then the return will get too hot before it has got to the rads and the boiler will cycle no matter what pump is on it.

Hence advising that the 8mm is replaced.

 

[Terrywookfit]

The filter stood up on a dog leg is doing you no favours with flow rate and is a potential airlock .

What is the delta t of primary and secondary pipes to PHE?

Is pump on Heat source maintaining adequate flow.
Is a flow restrictor fitted to coil in h/w cyl,

IS THIS A RECENT OR INHERITED PROBLEM ??