The pump will become noisier. Generally, TRVs don't close completely but reduce flow. If the system is set up reasonably, the main room thermostat will be stopping the CH before that is an issue.
That could have been the mechanism before.
Particularly, you want to know if a bypass is required when the system is fully pumped with no gravity and if there is a pump over-run thermostat
Oh. I was going to fit one just to be safe, but now it seems it wouldn't open (without pump overrun) even if I did!
I cannot find an e-mail address that works for Mistral so I will have to get in touch by post.
I used one of hose fan timers for a fan. I set it to 20 minutes; it ran for seven. The scale is very approximate!
But unless he has some means of over-running the pump [1], an automatic by-pass will never open.
[1] Either by pump control built into the boiler (unlikely), or using a timer as I suggested in another post
It's bad practice to have TRVs on *all* rads if that is your only temperature control because the pump will still run and the boiler will cycle unnecessarily on its own stat - both of which waste energy. You should also have a room stat which cuts *everything* off when satisfied - and the rad in the room containing the room stat mustn't have a TRV, otherwise there'll be a conflict. A by-pass is primarily to provide a path for the boiler to dump its heat.
With some boilers, yes. With your particular boiler, obviously not - 'cos that's how it's been happily operating in the past.
Indeed - but it should operate consistently once set. You can rig it up temporarily to switch a lamp or somesuch while you're adjusting it.
Yes I know.
I was looking at it from the perspective of reverse circulation - i.e. if it doesn't happen with a lockshield valve then no real problem.
OTOH, it might, and it would be less effort to fit an ABV in the first place.
He'd certainly be guaranteed no reverse circulation if the bl**dy thing never opened!
There is no TRV on the hall radiator (where the thermostat is) for the reason you describe, nor is there one in the bathroom. However I thought I had read here that some people do put them everywhere and this then causes trouble because the pump has nowhere to push the water?
I wasn't sure whether to split upstairs and downstairs and make two CH zones. If there is one rad without a TRv in each, will that be enough?
Thanks.
Enough for what? The pump will be happy enough - and wouldn't really mind if they all closed - it would just build up a bigger static head of water (since CH pumps are centrifugal rather than positive displacement types).
If you're asking whether having one rad open per zone will act as a by-pass (if, indeed, you need one at all) then the answer is NO - 'cos the zone valves will be closed at the times when a by-pass may be needed.
I have two zones (upstairs and downstairs) with two thermostats (lounge and main bedroom). The bathroom radiator is on a third loop which is permanently connected in order to dry towels. Other rooms have thermostatic radiator valves and we use no other heating under normal circumstances. The upstairs/downstairs split was done nearly 30 years ago when my wife was working from home in an upstairs room.
Geo
This is what I was asking about: the pump. I thought the whole point of keeping at least one radiator without a TRV was to prevent the pump from damage.
Have I got that wrong? Is the only reason you do not have TRVs on all radiators because you need one without by the thermostat?
If the pump does not mind, what is the point of a smart pump; is it just that a smart pump will be quieter?
Thanks.
That's what I have done. The hall rad has no TRV because of the thermostat and the bath radiator has no TRV to dry the towels. I do wonder whether I should add a TRV to the bath radiator because surely once the towels get dry and the room gets warm there's no need for any more heat?
Hi,
I was re-reading your post. I just wondered why can't it quite achieve constant pressure and is there any significance to that?
Thanks again.
Hello again.
I have quoted one of Roger's posts because he explains it better than I could:
Yes.
That's what I have done.
I have done this, so that what used to carry hot water to the upstairs radiators now carries hot water in the opposite direction to the downstairs radiators.
I was thinking that previously the downstairs radiators were nearest the boiler but now that they are at the other end of this pipe, they have moved further away. Does this mean that I need to re balance the system? Is there a danger that the upstairs radiators now being on a shorter pipe run will "steal" all the water from the downstairs rads?
I would like to keep the upstairs and downstairs rads on separate circuits. We discussed fitting a gate valve to the HW circuit to throttle that from stealing the CH water. I presume no gate valve is needed to balance upstairs versus downstairs CH since this could all be done at the lockshields?
Thanks.
I have moved the pump from the kitchen to the airing cupboard. As long as it does not keep me awake, that's where it will stay. When the pump was downstairs there was a lot of water above it. Now that it's upstairs there is less water above it, so do I need to be more concerned about sucking air down through the vent pipe? I'm wondering whether it would be easier for the pump to suck air through the relatively short vent pipe rather than suck water up from much longer the downstairs CH circuit?
I have connected 2-port valves set in manual override (I'm about to wire them; please see my other post). Last night the upstairs rads got hot but the downstairs ones were stone cold. I wondered whether this could be a factor?
The other thing is, the pipe work to the airing cupboard will be the highest point of the downstairs circuit, so do I need to add a bleed valve somewhere to let air out?
The strange thing is that this morning, the downstairs rads were beginning to heat, so I can't understand why yesterday they did not work and today they are! Any ideas what's going on?
Some of my rads are fitted with Aladdin automatic bleed valves from toolstation. For some reason when I refilled the CH these did not bleed and the manual override did not work either. I was very disappointed and had to manually bleed the rads with a spanner. Are these automatic valves a waste of time?
Thanks.
I have had a look at this and also the model for sale at Toolstation (order code 75473). The toolstation one has one fewer connections; why?
Yes, that - plus the fact that it will use less electricity when it throttles back.
If you look at the performance curves for a non-smart pump would will see that there are three (for a 3-speed pump) curved lines - each showing pressure vs flow for one of the speeds. Pressure is on the vertical axis, and flow on the horizontal axis. Each curve slopes downwards to the right, with a high pressure at zero flow and a high flow at zero pressure.
A smart pump, instead of running at one of the manually selected speeds, will automatically vary the speed according to the flow resistance it detects. But its range is speeds is limited to somewhere between the highest and lowest fixed speeds of its manual cousin - rather than being infinite. So, for example, once it's dropped to its lowest speed, if further restriction is imposed by (say) more TRVs closing, the pressure will start to rise and there's nothing it can do about it.
So, in summary, it varies its speed in order to *try* to produce a more or less constant pressure but outside its range of control it simply follows the pressure vs flow curves like an 'ordinary' pump.
Thank you.
It's quite likely that the balance will have been upset by the significant changes which you have made to the system.
I would balance the *whole* CH system - with both heating zones on and HW off, just by adjusting the lockshields - no additional gate valves needed. The, when you're only running *one* heating zone, the individual rads within that zone should remain reasonably in balance.
As far as balancing CH vs HW, its a suck it and see job. As I said earlier, if you can arrange the timing so that CH and HW are not usually on at the same time, so much the better. Otherwise start with the HW gate valve fully open and see if you notice any adverse effects on the heating when the HW is on. If so, throttle the HW back a bit and try to find a position where it still gets hot quickly enough without affecting the CH. I don't think there's a scientific way of doing it (like balancing radiators) because you never have steady state conditions when heating the HW.
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