Some heating circuits not working well - what to do..?

[gaz1]

This radiator balancing malarkey in domestic systems has never sat comfortably in my mind. I'm not saying that it doesn't work at the time it's done, because it does work, and is necessary if there aren't any TRVs on the radiators themselves. But, in the longer term, the flow restriction can be a place where blockages can occur. It only takes a couple of lumps of magnetite, or some other contaminant, larger than the size of the restriction, to lodge at that point and start the blocking process. I prefer systems where there are TRVs on every radiator, except one, lockshield valves more or less open and, once a room comes up to temperature, the TRV reduces the flow to the rad, allowing a greater share of the flow to reach the remaining radiators on the circuit. Yes, the room(s) with the initially flow-starved radiators take a bit longer to reap the benefits, but they get there, usually within half an hour, or so of the heating coming on.

A thermal camera can be very useful for visualising heat flows in radiators.

Out of interest, does the system gurgle much when it's on?

if set to open all your heat rushes upstairs and therefore the heat downstairs is poor

it also rushes to the closest point and returns via that way so a long distance rad remains cold so balancing is the required remedy

slow the flow to upstairs then feeds the heat downstairs the same can be said for the longest distance away from the boiler

even the hot water cylinders have to be balanced otherwise the full flow goes through that and back to the boiler on the quickest shortest route

trvs only control the flow until that room becomes warm enough then shuts down then feeds the other rads but that means your central heating needs to be on for a full hr compared to 15-20 mins and all rads up to full temp when the system is balanced properly

As for crap in the system – fit a filter, use inhibitor. My filter pulled an enormous amount of crap out of the system in the first few weeks of having fitted it, then pretty much nothing from then on.

the inhibitors can and dose block the system where the valves are set lower on the return flow as some inhibitors have a sealer within them for sealing small leaks

get any sludge or small particles that build up and it acts like a small leak of water and thats where the sealer starts to block the flow

opening and closing the return valve dislodges this effect if you open and close that valve a few times and then reset the valve to the same point

 

[gaz1]

So, with only the pump to the manifold connected and all rads on that manifold turned off other than the furthest most troublesome one, the furthest rad still took an age to get warm - basically ALL the hot water was being sent to it. I mean its been on maybe 15 mins and the return at the manifold is barely warm, the radiator was starting to get warm. Pretty sure there isn't air in it as have flushed it with a hose to clear that.

In my head, it suggests an issue with the pipework? Could be the pump perhaps but it seems to draw hot through to the manifold. But if the pipework is at fault, why, if i connect the pipework up to a hose on the cold tap (isolate the manifold from the system and stick a hoselock on the end of the flow and return manifolds), do i get good fast flow and not a lot of crud?

depending on the model of rayburn you have its from 3 rads up too 20 rads on the system it can run

at 15 mins the return flow will still remain low heat only the rads will become red hot a longer time and that return flow will become hot

so you have run all 4 rads at one at a time so anything thats there is flushed enough through the system including that troublesome rad so it becomes hot

if after 15 mins and that troublesome rad hasnt warmed up in that time then you have an issue with blockages via either sludge air lock somewhere on that line
just warm house up for tonight

redo the test again only on that troublesome line at full flow tommorow shut down the other rads unplug the other pump again and turn on that line again if still not getting red hot there is def trouble on that line

 

[reb78]

depending on the model of rayburn you have its from 3 rads up too 20 rads on the system it can run



redo the test again only on that troublesome line at full flow tommorow shut down the other rads unplug the other pump again and turn on that line again if still not getting red hot there is def trouble on that line

Mines the biggest output Rayburn for solid fuel (or was back in 1990) - Rayburn always quoted 12 rads on this model IIRC which is a little under what I have but it heats a large airspace in my place so it's probably about right in terms of rads.

It's getting the heat to the furthest places via the rads that's proving hard

The last test is what I describe above. Just that one rad on. I don't understand why I can get a good fast clear flow with a hose yet the pump won't get heat there when that's the only rad available to circulate to.

 

[reb78]

This does suggest a blockage of some sort in that particular radiator, or its pipework, though you say you've ruled that out. Presumably there's not any underfloor heating, or other type of "heat sink" on that radiator circuit, since you said previously that various bits have been added by the previous owner, over the years.

No underfloor heat. And I dont think there's another heat sink if I turn the pump off to the 12 rads and just use the one to the manifold with only the most troublesome rad open.

 

[reb78]

When you shut everything down and just run that one rad does the return to the boiler get hot or nothing?

I don't think it did but will double check. As far as we can tell, the pipes run from that manifold to the rad and back to it.

 

[voipio]

if set to open all your heat rushes upstairs and therefore the heat downstairs is poor

Not found that to be an issue in modern properties, at least. The pumping capacity of central heating pumps is considerably greater than the tendency for water flow induced by natural convection towards upstairs rooms, so this phenomenon only plays a minor part in the overall flow distribution.

 

[reb78]

Not found that to be an issue in modern properties, at least. The pumping capacity of central heating pumps is considerably greater than the tendency for water flow induced by natural convection towards upstairs rooms, so this phenomenon only plays a minor part in the overall flow distribution.

Mines very much the opposite too. Downstairs rads are fine. All on this manifold are upstairs in bedrooms and bathrooms.

 

[voipio]

The last test is what I describe above. Just that one rad on. I don't understand why I can get a good fast clear flow with a hose yet the pump won't get heat there when that's the only rad available to circulate to.

Could there be a non-return valve in circuit? Water from a hose would get past it easily, but the pressure generated by a central heating pump pump might not be sufficient.

 

[addjunkie]

Could there be a non-return valve in circuit? Water from a hose would get past it easily, but the pressure generated by a central heating pump pump might not be sufficient.

On the radiator slow to heat up, have you taken it off, removed the valves and shoved a high flow hose pipe through it, its amazing how much crap you get out of them.

 

[reb78]

On the radiator slow to heat up, have you taken it off, removed the valves and shoved a high flow hose pipe through it, its amazing how much crap you get out of them.

Yes. This I have done. Twice in 7 years (as its always been bad). First time I got a fair bit out. Ran the pipes without the rad on until they were clear and put it back on smug I'd fixed thr issue - but the smugness faded quickly as I realised it had made no difference!

The last time was earlier this season. Not much came out tbh.

 

[reb78]

Could there be a non-return valve in circuit? Water from a hose would get past it easily, but the pressure generated by a central heating pump pump might not be sufficient.

I don't think so from what I recall of the pipework I have seen.

 

[Mark 5]

So, with only the pump to the manifold connected and all rads on that manifold turned off other than the furthest most troublesome one, the furthest rad still took an age to get warm - basically ALL the hot water was being sent to it. I mean its been on maybe 15 mins and the return at the manifold is barely warm, the radiator was starting to get warm. Pretty sure there isn't air in it as have flushed it with a hose to clear that.

In my head, it suggests an issue with the pipework? Could be the pump perhaps but it seems to draw hot through to the manifold. But if the pipework is at fault, why, if i connect the pipework up to a hose on the cold tap (isolate the manifold from the system and stick a hoselock on the end of the flow and return manifolds), do i get good fast flow and not a lot of crud?

Because imo, there is no blockage, at least in the pipework,, as I said, different pipe sizes and your pump/s set up is not helping but even that against you, correct balancing will improve the situation..

 

[bricol]

the inhibitors can and dose block the system where the valves are set lower on the return flow as some inhibitors have a sealer within them for sealing small leaks

get any sludge or small particles that build up and it acts like a small leak of water and thats where the sealer starts to block the flow

That's not how sealants work - they need contact with air to polymerise.

But if I'd meant "sealant", or any form os sealer, I probably would have said "sealant" .

 

[JimmyS]

When you had the ufh manifold pump running on its own and the other pump turned off and all the flow directed to the one radiator, did you check the temp of the water going into the pump as the flow temperature might have been diluted with water from the pump that was off flowing in reverse. Worth checking as you might have had flow to the radiator but the water might have been cool.

 

[jsf55]

Have you checked the valves on the rad actually work ? would it be worth changing them out ?

 

[Kayos]

Manifold needs a close coupled tee, and lose one of the pumps (not the one feeding the ufh)

 

[JimmyS]

The last test is what I describe above. Just that one rad on. I don't understand why I can get a good fast clear flow with a hose yet the pump won't get heat there when that's the only rad available to circulate to.

The hose might be working at 3 bar pressure whilst the wee grundfos pump can probably just manage 50kpa at virtually closed valve condition, but as you say would expect some flow from the pump.

Have you checked both flow.and return are OK with your hose?

If both OK then maybe try disconnecting rad valves from radiator and fitting to pipework and checking you are getting flow through the valves in case one of them is blocked. If both valves OK then take radiator off the wall and run the hose through it outside make sure it's OK and not full of crap.

 

[reb78]

When you had the ufh manifold pump running on its own and the other pump turned off and all the flow directed to the one radiator, did you check the temp of the water going into the pump as the flow temperature might have been diluted with water from the pump that was off flowing in reverse. Worth checking as you might have had flow to the radiator but the water might have been cool.

Yep. Boiling hot. So definitely hot water getting to that and the manifold

 

[reb78]

Have you checked the valves on the rad actually work ? would it be worth changing them out ?

Definitely clear. Not long had the rad off and ran them both to check just this.

 

[reb78]

The hose might be working at 3 bar pressure whilst the wee grundfos pump can probably just manage 50kpa at virtually closed valve condition, but as you say would expect some flow from the pump.

Have you checked both flow.and return are OK with your hose?

If both OK then maybe try disconnecting rad valves from radiator and fitting to pipework and checking you are getting flow through the valves in case one of them is blocked. If both valves OK then take radiator off the wall and run the hose through it outside make sure it's OK and not full of crap.

Done all this.

I take the point about hose pressure vs pump though