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  1. UKenGB

    UKenGB New Member

    These seem to no longer be available (unless anyone can let me know from where I could get one) so...

    Could anyone help with how to use 2 independent pumps (one for DHW and other for CH) and eliminate the need for any motorised valves. Surely someone must have worked out suitable circuits, both electrical and pipework?
  2. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    You can use the new heads if it's just the motors that have gone
  3. Gasmk1

    Gasmk1 GSR

    Low loss header
  4. Ric2013

    Ric2013 Plumber

    My guess: 2 pumps, possibly check valves to put a bit of resistance to induced flow if the pipework doesn't prevent this, run a relay off the switched lives powering pumps and run permanent lives to relays so the relays can switch on boiler?

    Not sure how you'd get the boiler to action pump over-run, if required.
  5. UKenGB

    UKenGB New Member

    I'm still thinking about this and having obtained the required replacement boiler, need to finalise my plans and could do with some basic advice.

    First of all, pipework.

    The boiler is a Worcester and has 4 connections. The old one used 2 for the pumped CH and the other 2 for gravity DHW. I'm thinking of keeping that basically the same, but adding a second pump for the DHW side. Questions:-

    Is it better to have a pump on the flow or the return side of the boiler? I've seen both schematics, but is there an accepted wisdom that either is a better solution?

    As this is an open vented system, where best to connect the feed and vent pipes, i.e. in relation to the pumps, NRVs etc.

    Is it acceptable to have the pump(s) above the boiler, i.e. in a loop with a high point, but use air bleed valves at the actual highest point? The problem is simply space and where I can best fit in the pumps.

    Should automatic bleed valves then be on the pump outlet sides?

    I intend to use NR/check valves to prevent unwanted flow when pump is off. Where best to install these? At the inlet, or the outlet of the pump(s), or elsewhere?


    Since no zone valves, would it be considered acceptable to simply power the boiler and pump(s) simultaneously. No need for any sort of interlock, like only power boiler when pump is running (although how could you even do that).

    Would an oil fired boiler in this scenario require some sort of overrun on the pumps after the boiler shuts off, bearing in mind there will be no actual zone valves?

    I have a pretty good idea about all the above, but it's always nice to roll such ideas past others who are more likely to spot flaws and be able to offer additional advice.
  6. Ric2013

    Ric2013 Plumber

    No need to interlock boiler? I think Part L of the Building Regulations would strongly disagree.
  7. UKenGB

    UKenGB New Member

    Could you explain what you mean and how you would arrange an interlock between the boiler and pumps since there is none when zone valves are used. The interlock exists to prevent pump and boiler powering on if the valve remains shut, but when the valve opens, the boiler and pump are simply powered on together are they not, no interlock between them, so either could not work but the other would still be powered. However, since the valve is open, this is obviously not a problem.

    In my case, there will be NO valve and nothing can be closed. So why would this need any sort of interlock when those 2 devices do not need it when zone valves are used. And how could you do it? Only power the boiler if the pump is actually running? How would you be able to determine that. To the best of my knowledge, circulation pumps don't incorporate any sort of feedback regarding their operating status, unlike zone valves that have to do so for obvious reasons.

    As far as I can see, when the programmer/thermostat(s) call for heat, the boiler and pump would simply be powered simultaneously. Or is there something I'm missing there?
  8. Ric2013

    Ric2013 Plumber

    Part L is about energy efficiency. Thus having a boiler running just to keep itself warm is considered wasteful. If I understand rightly that you are building a new system using a boiler that isn't going to meet the energy efficiency requirements, you'd be in breach anyway, but since you will be paying for the oil, you may as well have effective controls.

    'Boiler interlock' is a technical term that basically means that the boiler is not running just to keep itself warm so when there is no call for heat the boiler shuts down. There isn't a specific 'right' way to do this.

    Since zone valves incorporate a microswitch that only fires up the boiler/pump when the valve is open (in effect, the zome valve doubles as a relay), you are wrong to state that there is no interlock when zone valves are used. And while it is true that interlock prevents pump and boiler powering on if the valve remains shut, the point is to avoid the boiler running wastefully. Some of the old gravity boilers will happily fire up with no flow whatsoever and sit there just keeping themselves and the chimney warm, provided there is provision for expansion of the water in them, but this isn't the object of running a boiler.

    What I can't understand is how you are going to run your pumps independently of one another if the pumps and the boiler are all powered up at the same time and you don't want to use relays. To me, from the way you've explained this, it sounds like you are committed to having both pumps and boiler run at the same time whenever any of your thermostats call for heat.

    The other problem is that, in my view, you aren't asking for general advice. Where to connect vent and feed pipes and pump is covered on about a million diffrent websites, but what do the boiler installation instructions require? Also, a lot depends on site conditions and if you are aren't going to get a professional to design this for you, then you are the only one with in-depth knowledge of this.

    Two people other than me have given you advice which you have simply disregarded and gone on to say that what you intend to do is completely different. Remember they are giving up their time for free and I suspect they have less time on their hands than I do. That said, I have quotations to write myself :)

    Do let us know how you get on though, it is always interesting to watch these slightly unconventional projects progress. Sometimes they work very well. Mine did!
  9. UKenGB

    UKenGB New Member

    First of all, I am always appreciative of actual advice given when it applies to the question I asked, but that doesn't mean I'm going to blindly follow what's been said. As you rightly point out, only I know the intricacies of my system and what I actually want to achieve.

    There's a problem here with semantics. I'm not a professional plumber and although I've done a lot of plumbing in the past for myself, I'm not necessarily going to understand the exact meaning of terms that are used, even though I would understand the underlying principles if I knew to what they were referring.

    Case in point, 'interlock' to me means preventing interconnected systems from operating in a way that is undesirable, dangerous even. Hence I applied that to mean the use of a trip switch in a zone valve that is then used to power the pump and boiler. In this way the boiler is prevented from operating unless the zone valve is open. The idea of this actually meaning only running the boiler when either the CH or DHW systems are calling for heat makes no sense to me as I would have assumed that was a given.

    So, to clarify, I really would just like to use a Grundfos Pump Plan. Unfortunately, that is no longer available so I will have to cobble together an equivalent and I hoped others on here would have a good idea of how to do that and advise me, hence saving a lot of time trying to work it out from first principles. Rather than simply ask for someone to do it all for me, I was trying to just ask specific questions whose answers would then enable to me to complete the rest.

    I don't think I said I didn't want to use relays, but if smart circuit design can obviate their requirement, I'm all for that as they're just a device that can go wrong. However, if I need to use any, so be it. I've designed plenty of relay circuits for vehicular use when the need arose.

    I also did not imply I wanted or even accepted that both pumps would always operate simultaneously. That would be daft.

    However, rather than try and replicate the original Grundfos PP wiring centre (tricky with no information on how it functioned), it occurred to me I could probably make use of the current Honeywell Wiring Centre (HWC) which already has suitable connections for everything and is currently configured for a C Plan system, i.e. pumped CH and gravity DHW. Which leads me to answer the question about how to run the 2 pumps independently.

    The HWC has the obvious connections for (and is already connected to) the boiler, thermostats, programmer and CH pump etc. It also has connections to a (currently 2 port) zone valve for the DHW circuit but which is being eliminated. My idea is to utilise these zone valve connections to instead drive the DHW circulation pump (another Grundfos) The HWC takes care of only 'driving' that valve when the DHW is calling for heat and that is precisely when the DHW pump would need to operate.

    Just hook up the additional pump to those zone valve motor connections (normally Blue and Brown) and instead of its microswitch, use a CO relay (COM = Orange, NO = Grey and NC = White) powered by the feed to the associated pump (COIL = Blue & Brown). In this way the boiler is powered when EITHER the CH or the DHW (or both) is calling for heat, but not otherwise. Everything else can remain the same.

    But still a couple of points I'm unclear on and could do with some specific advice:-

    Should the pumps be on the Flow from, or the Return to the boiler?
    Normally it could be either, but I suspect that using 2 pumps in this way, it probably needs to be as shown on the Grundfos diagrams with pumps on the output Flow from the boiler.

    Where then would the NRVs need to be?
    I think the Grundfos Pump Plan has them on the pump inputs, but it's hard to tell. That makes sense to me so is that where they should be?

    Is any 'pump overrun' required? Don't think my current boiler is connected for this. Should it be?
    Last edited: Sep 18, 2017
  10. UKenGB

    UKenGB New Member

    Thinking on this a bit further:-

    The current boiler has 4 connections, 2 of which are used for CH and the other 2 for DHW. Assuming the replacement boiler has the same 4 connections (same manufacturer and model) I see no reason to change this setup.

    The CH pump is currently in the CH Return so I reckon I could simply add the other pump in the DHW return and all other connections remain the same. Then the NRVs could be almost anywhere, just to stop any gravitational flow when that pump is off.

    Any obvious flaws in this?
  11. Ric2013

    Ric2013 Plumber

    My point was that, 'boiler interlock' to me, was a specific technical term, hence the confusion, now clarified.

    Sounds like you're working your way through it though.

    I would object that 2 zone valves and one pump is cheaper than two pumps (and you already own one of each), but you may have a spare pump as well and not want to modify pipework more than you need to.

    Just make sure the boiler has nothing restricting its ability to access the vent (and feed) pipes at all times. No valves between them and the boiler. Pump over-run will be required if the boiler installation instructions require it and the boiler itself will usually control the pump in this case. Not all boilers require a pump over-run, so you will need to refer to MI's.

    If you are using plastic piping, bear in mind that a heavy cast-iron boiler can retain a lot of heat and throw a slug of very hot water when it starts up, if it has recently shut down and sat unpumped (eg if DHW shuts down just before the CH room stat calls for heat). In this case, pump over-run could be useful to dissipate the heat after the boiler has finished firing, possibly with a pipe-stat controlling this.

    I'm not old enough to have been around when this was common, but my understanding is that pump on return was the old way of doing it, preferred as the pump is running on the cooler return water. It worked as long as the boilers had minimal resistance to flow and the system open vent was connected to the boiler flow with the feed pipe connected to the boiler return, making the boiler 'the neutral point' i.e. at atmospheric pressure.

    I'm assuming you will have an open-vented system with this kind of setup? Modern boilers often have higher resistance and so this form of plumbing started to cause problems with water being forced up the feed pipe when the pump ran. Also, the fact that water is being sucked around the system with a pressure below atmospheric meant that any small defect would result in a lot of air being sucked into the system. So boilers then started to be close-coupled: the vent teeing off the boiler flow, followed closely by the feed teeing off, followed by the pump on the flow.

    I once reworked the installation for an old semi-gravity system with very old low resistance boiler in my own home, long before I trained as plumber (we are a bit alike, I think) and made an S-plan-plus. I first close coupled, with the pump on the flow, and this worked well. I later managed to get hold of the MI's and found that close coupling was not a recommended method (probably as there was no manual-reset overheat thermostat on the boiler) so I left the pump on the flow, but moved the vent and cold feed to the flow and return on the boiler (the old way), making the boiler the neutral point. This also worked, and seemed safer to me (and didn't conflict with the MI's). That said, when a gas installer, servicing the boiler, decided to wrench it around because he felt it wasn't quite straight (the mind boggles), there was air ingress for some time due, presumably, to the very poor state of the iron couplings on the boiler primaries.

    I think you're barking up a reasonable tree (though I think you should consider using an S plan arrangement now that modern pumps have proportional-pressure control). With the pumps on either the flow or return and boiler as neutral point, you risk dragging air down the vent and pumping up the feed, but if the boiler instructions do not allow close-coupling, then either pump on flow or return is probably acceptable to my way of thinking, flow being preferable, and, from what I can gather about you, I'm sure you'll be setting the pumps to appropriate settings, not defaulting to maximum (it happens often). I'm not the most experienced person on this forum regarding these matters, but I hope this helps.
  12. Ric2013

    Ric2013 Plumber

    NRVs - pump inlet seems reasonable, but if there is any chance of hot water rising up and down the same pipe on the flow, then I'd put them just after where the two flows divide. If pumping on flow, this might be the same thing.

    EDIT - I'm concerned that the NRVs may cause problems with your venting arrangement, dependent on design. Please come back online when you think you've worked out the rest of the system.
    Last edited: Sep 18, 2017
  13. UKenGB

    UKenGB New Member

    Thanks for that. I'll need to read it a few times to fully digest. A bit of background:-

    The current installation is as I said C plan (open vented), Worcester Danesmore (NO pump overrun) with pump on CH return. Currently on oil, but hope to be gas next year although unfortunately the boiler just gave up (water jacket ruptured). So intense annoyance aside, no point in making big changes or buying a new boiler that may come out in a year's time.

    We've found another same model Worcester, used, so the price is rather more acceptable and it's likely it'll mostly connect straight up to the original pipework. But, DHW has never been efficient as the cylinder is at the same level, just the other side of the wall behind the boiler. Also, I have had incessant trouble from the Honeywell 2 port zone valve. After replacing the motor about 5 times over the years, I gave up and just use a relay to keep the system working. So, I'd like to eliminate zone valves and just use a 'pump plan' type system which will also provide much better flow in the DHW side.

    At the moment, apart from switching to pump plan, I want to keep the changes to the minimum and get the boiler installed and the system up and running ASAP as it's getting cold. Next year, if we switch to gas that'll be new boiler and install done at a time when I can totally revamp, but for now, I want the simplest working solution.

    Which means if I can keep the pumps on the returns, there's a lot less to have to mess with. Just add the pump on the DHW return side where there's plenty of room. My mod to the Honeywell Wiring Centre means not a lot of work to be done there and it'll be easy to add the wireless room and rad stats I want, to enable Apple HomeKit control. The connection box fits onto the std. programmer backplate already wired into the HWC and which is essentially vacant as the old programmer recently also gave up the fight.

    So it's optimise what I can do now in the shortest time, but plan to make improvements when new gas boiler gets installed in the near future.

    Now I'll just re-read what you said :)
    Last edited: Sep 18, 2017
  14. Ric2013

    Ric2013 Plumber

    To be honest, and from the information I've absorbed, I'd be tempted to do the same.
  15. UKenGB

    UKenGB New Member

    As always, more thinking means more changes to the plan. The problem I have is with the vent and feed connections. With both CH and DHW circuits being independently pumped, I need to re-think where these will be. Also, I want to change the main connections to the boiler for the CH from the current 22mm to 28mm and then T off at 22mm for upstairs and downstairs circuits. So this means first taking out the current 'pump on return' pipework. In which case, I might as well change to 'pump on flow' as this is currently the preferred (and presumably better) arrangement.

    There are however some other factors (physical locations and access restrictions) to be taken into account, for which reasons it would make sense if I could do the following:-

    The boiler has 4 connections, 2 x flow at the top and 2 x return at the bottom. I want to maintain the current arrangement of 1 x pair for DHW and the other pair for CH (each circuit with a pump of course). With that in mind I thought to fit a vortex type air separator on the CH flow output, connected to the vent and of course on to the CH pump.

    But rather than have the feed connected close by, I thought I could connect that at the same point in the DHW circuit, i.e. in between the boiler and pump, but at a lower height than the actual boiler flow outlet.

    In this way, the vent should work with the air separator as intended, purging the system of air and in particular, helping to prevent air being pumped around to the rads. The DHW flow drops from the boiler output and so should be clear of air and the feed is then connected on the pump input side and hence little to no chance of pump over.

    With the feed tank a good 5m above the boiler, I cannot help but see this as a good working solution. Would anyone comment otherwise?
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