Hot radiator

Presumably it's plumbed on the hot water circuit, but the question is why? Don't suppose, in the way of old houses, that room has ever been used as a bathroom? Sometimes towel radiators are put on the DHW circuit (if you're running the hot water you might be having a bath, so warm towels are good).

Is the tank on gravity feed (ie the pump doesn't run when in hot water mode, it just works by convection)? Maybe there's some reason to have a least one radiator to make enough 'cold' water for the thermosyphon to work properly?

Theo

It is probably on the thermal siphon circuit then. This was common practice when there was a back boiler on the fire in the living room so that hot water and one bedroom could be kept warm even without mains power. It is essentially a way to dump heat out of the back boiler to prevent it bumping. You can't run the fire quite so hard when the pump isn't on. Mine is on a thermostat so that the CH pump will come on once the hot water tank is more or less up to temperature. Now burning entirely solid fuel now thanks to the stratospheric price of oil.

My wood burning stove with a back boiler has exactly the same configuration. It dumps heat into a radiator in the master bedroom and the hot water tank in the event that there is no electricity.

Invaluable when our UK electricity supply has become so third world.

It is the hot water syphon path that remains active without the pump - a configuration that ISTR is now no longer approved for new installs of oil or gas boilers. You are supposed to have a 3 way valve nowadays.

It could be due to several factors.

I assume you have 3 way valve or equivalent. They can stick, allowing heater water in the primary circuit to pass even when not wanted. Even without a pump, you will get some circulation - some older, simple, systems didn’t have pumps. *

Then there is the layout of your pipes, lock shield settings etc. The radiator getting hot - while not obviously nearest the ‘system’ may have better pipe work - wider, less bends, etc.

There is no three-way valve. And I believe that the radiator in question is plumbed into the same supply and return lines as the more distant radiator further down the line. I will recheck that, though. I am still not sure what is going on, if this is correct. But being in the primary loop really does seem to be the only answer. Thanks, everybody, for the thoughts.

The hot radiator is on the same pipe pair as the cold radiator further on. It is a lot closer to the tank, though, maybe 2/5 of the distance from the tank to the distant radiator.

The lock shield valve setting is the other factor. In fact, that is their purpose- at least before the days of thermostatic rad valves.

Without trying to teach you to suck eggs, one valve is simply to turn the rad on/off. The other is to ‘balance’ the system - basically ensure all the radiators get a share of the hot water flow the primary circuit. Opening/ closing them different amounts compensates for the pipe lengths, bends, upstairs vs downstairs, ….

Once set, you generally don’t adjust them again. They can be set by using a pair of thermometers and looking for the same drop across all rads ( I forget the number). Or, as most people do, all rads feeling about the same and the rooms feeling right.

Our house has some long pipe runs due to the layout and some of the valves are hardly open. That said, we have thermostatic rad valves in most rooms which tend to correct any imbalance.

Yes, indeed. All the radiators in the house have TRVs, and I will admit that the lock-shield valves have not been changed in at least 14 years, since I moved in. But the TRV setting takes care of the day-to-day running, anyway. What I might do is to raise the setting of the TRV of the distant radiator, temporarily, and see what happens to the heat output. And maybe open up the lock-shield valve to see if it has any effect under the normal conditions that produce heat in the first radiator. That might not be a priority job, though. But thanks for the thoughts, they are all useful.

It is worth checking the TRV valve isn’t stuck if they don’t work.

Remove the ‘head’ and press the ‘pin’ down with a bit of metal. If it doesn’t move or is stuck down, a tap with a hammer usually frees them. Refit the head.

Been there, done that. But both of these radiators control temperature ok, so there doesn't appear to be that problem. I find that most of my TRVs need to be woken up as described as winter approaches.

More egg sucking, but just to clarify that the TRV doesn't affect heat output (ie watts), it just sets the temperature at which the rad turns off. The lockshield is what sets how many watts you get out of the radiator when it's turned on. Unless the TRV is off, twisting it won't change how warm the rad feels.

Crudely, the lockshield sets the watts and the TRV sets the watt-hours. (if the external conditions were constant).

Also, some TRV fittings have a built in lockshield valve - so it's not always at the opposite end to the TRV.

Theo

When the heating season is over, I turn my TRVs to the maximum setting, to avoid the valve seal being pressed onto its seat for months on end.

If it gets stuck in that position, rather than stuck shut, at least it’s easier to encourage the pin to go down rather than to have to pull it up.

Good advice, I do the same. I also helps with the first ‘air bleed’ when you fire the system up for the winter. While, provided you have still active inhibitor in the system there shouldn’t be much ‘air’ in the system there is usually a bit. Just enough to give an annoying gurgle 😀 in the morning.

Emptying the system every few years and running cleaner through is worth it, including cleaning the header tank if a vented system. I confess I missed doing ours- I had a bad knee and getting to the tank a few years back. The result was a blockage where the pipe from the header tank joins the main pipes. Needless to say it happened when it was darn cold! Not a huge job to fix but a pain to do.

Good point, although if the lockshield is set too low ( not enough flow) the overall system thermostat (room stat, if you have one) may turn the system off before the rad stat cuts off. Getting them to work in ‘harmony’ can take time.

We have a Hive main stat and I’m considering changing the TRVs to Hive heads but the Hive heads are probably the most expensive on the market. We’ve a lot of rooms. While the Hive system as is has proved a money saver, I’m not convinced adding the Smart TRVs is worth it.

My system is a heat store and radiators that share the same water, with DHW provided by a plate heat exchanger.

I clean out the header tank twice a year and add inhibitor. It’s very noticeable that my neighbours that do this still have the original system in place, now 20 years old, and those that don’t have suffered corrosion in the heat store, replacing it with a combi boiler.

One advantage of the heat store is that within a minute or so of the thermostat calling for heat, the radiators are piping hot, just what one needs on a cold day.

Our system burns half its annual gas consumption in the period December, January, and February; statistics suggest that that is the time something in the heating will go wrong…

Some installations had a simple thermosiphon primary loop in the hot water cylinder and a pumped circuit for the radiators. If the pipework arrangements were not carefully routed some hot water could rise in the radiator circuit and patchy instances of upstairs radiators could get hot without the pump running simply because of unwanted thermosiphon effects. Depending on the pipe geography a spring loaded non-return valve in the return leg provided enough resistance to stop the thermosiphon effects but would open when the pump exerted greater "push" to the circulatory path. Another possible effect might be using a common return pipe shared between the hot water primary and upstairs radiators. Again depending on the pipe geography strange things can happen. Finally some systems use an abortion called an injector tee which can create undesirable effects such as you have. I'd suggest you read up on the "standard" systems such as C-plan, Y-plan and S-plan then consider some basic pipe alterations if necessary

Thank you for that. I mapped the pipework as well as I could without pulling up floorboards when we moved in to the house, and what I can see in the airing cupboard and near the radiators looks conventional, a standard single valve to the radiator circuit, 'C' Plan, I believe. There is no sign of shared pipework that I have seen. But some pipe runs are covered, but I see the ends of the runs, and they look correct. Whatever the reason, I have no plans to change it, as I found it very useful when the pump failed, as I described in my Original Post. I just wanted to to understand it.

I'm not convinced that 'smart' TRVs are that useful. They allow you to tweak the setback temps (eg drop the temp at nighttime) on a room basis, but do people really want to do that over just tweaking the main thermostat? I see the sales pitch of having a 'dashboard' to control everything, but do people really use that?

I had some Radbot TRVs which were quite neat: they had a light sensor so would increase the temp when it detected room occupancy, and a button you could push to say 'I'm cold, boost the temp' (for 30 mins per press). That seemed to fit in better with actual usage, rather than an app that nobody opens after the first week.

But they didn't talk to the boiler so they couldn't bump the temps if the main thermostat had told the boiler to turn off. The units had a radio that could communicate but they never implemented that bit.

I could see the advantage of a dashboard if you have a big house and want to, say, warm up the West Wing when you have guests. But I suspect most people set their rooms to a chosen temp and just leave them, they don't actually want much smartness, and they wouldn't put the effort in to make use of it if they had it.

Theo

I live in a modest, reasonably well-insulated semi. I tend to spend much of my days at my computer, which is in the south-facing dining room which is adequately warmed by the sun for much of the year. The lounge does not need heat when it is empty during the day, or is being warmed by the gas fire.

My partner has an office in the third bedroom, but only uses it irregularly.

I have used some add-on TRV controllers with wireless stat, which worked reasonably well, but the base TRV eventually failed open. The lack of a call-for-heat signal is another issue.

Long-term there is an argument that I should have some form of intelligent valve, with remote thermostat and the ability to call for heat, but this is quite an expensive solution, and developments are still ongoing.

Since the kit I am aware of generally makes use of the existing valve, just screwing on a control unit, then it seems to me that the most important first step is getting working valves, that would be up to the task, which my existing Bulldog ones demonstrably are not.

I could then continue with a mix of standard TRVs and my existing control units, until I was happy about the cost/ benefit of a "Smart" system.

I know that TRVs are supposedly interchangeable, but I am loath to risk diving in to replace them myself, since any issues making them watertight with original olives, or lining up with existing pipework, could leave me without a working heating system.

Chris

I have Drayton (Now schnieder) Wiser. Its great. Bedroom is warm at night, cold in the day. living room warm during the day, cold at night.

Rad valves do talk to the boiler so boiler only kicks in when needed.

Once the schedules are set its no effort.

System also adjusts for outside temps so comes on earlier if its cold

I am sure I save money. Not sure I have recovered the cost of the system

Dave