Struggling to go fully pumped

[Gerontius]

I'd be grateful for some professional advice - can't think my way any further on this.

We have old-style vented gravity DHW and pumped CH system with little in the way of controls. Boiler is only 6 years old and fine, and I prefer to stay vented. There are reasons why I have to upgrade the whole system, but first step is to go fully-pumped to improve cylinder reheat and get abreast of current regs.

The difficulty in replumbing/rewiring is access. The boiler and pump for CH are on ground floor alongside programmer. The cylinder is on the first floor. The pipe (and cable) run to the cylinder is inaccessible, sealed into a five metre wide flat roof.

If I move the pump into airing cupboard by cylinder and fit a Y valve, I can’t get a cable to it from the boiler. I looked at the Grundfos twin pump (‘Pump Plan’) which has a dedicated Danfoss wireless kit for control, but this still needs wired connections to the boiler.

I am thinking maybe I could fit the twin pumps on the primary and CH circuit at the boiler, but this couldn’t be on the flow which runs up to the vent and feed. Is it feasible to fit it on the returns, despite the negative pressure this would make? I know this is not good practice. Or will I just have to remove some plasterboard to get into the roof space?

Also - I’m surprised the system was ever built like this since it has 5 metres of near-horizontal pipe on the flow/ vent – is this a big problem? (It’s been there since the 1970s.)

 

[fizzput]

What are your reasons for having to upgrade the whole system???

 

[Gerontius]

I was afraid that might be a question! We are revamping the bathroom where the cylinder sits, so it seemed a good time. The cylinder has to be moved several feet. It is uninsulated, and only about 130 litres. We have no controls on the system - no cylinder stat or valve on the rpimary return. We have heat leaking into the upstairs radiators from the DHW. Just reflects a time when energy was cheaper. Also F&E tank and cistern will have to come down from attic, so I was planning on switching to a thermal store arrangement for hot water - with rapid reheat cylinder transferring heat to mains pressure hot water, whether by a secondary coil or plate heat exchangers. We have about 3 bar of presure. This would only need a small F&E tank at the top of the airing cupboard. That's the plan! anyway. I wouldn't be doing the work myself - I plumb, but only at floor level, for physical reasons.

 

[sambotc]

can you not run additional wires surface in trunking? i know cosmetically it's not the best but would save you alot of money and hassle. Then use the gravity circ's for primary flow and return with s plan, that should stop the heat leak to other rad's unless they are piped like that intentionally

If you wait until you put in the thermal store the cold feed and vent could go in behind the pump on the primary and right up to the f&e so you can cut out the existing also?


Sam

 

[Gerontius]

Yep, the Boss in the household might not be happy, since the area in question - Sod's Law - has just been redecorated, but maybe I need to put in a ceiling conduit or a bit of disguising cornice. Means drilling through a 4 inch block wall and a solid 13 inch brick wall, but hey ho. I guess we would have the pump and Y valve - or even the Grundfoss twin, which looks really macho - in the airing cupboard by the cylinder, and just run a cable back down to the boiler.

Now I have thought about it, I'm concerned that the flow/ vent runs horizontal from the boiler. I thought it was supposed to be close to vertical. Is this a problem? Could be well sludged after all these years.

 

[Gerontius]

If anyone is still passing by this thread, I'm now concerned about near-horizontal length of the vent pipe. This is 28mm flow and vent from boiler. Altogether it makes a vertical rise of c 4metres, but runs near-horizontal for over 5 metres - and goes through five 90 degree elbows. It's been like this since install in 70s, but that's not much excuse.

Can it be left? I can't build a second-storey above the boiler. I don't want to move the boiler into the living room, below the cylinder. I didn't want to abandon a vented set-up, but would the only other answer be a sealed system? - which boiler would support.

 

[sambotc]

Don't worry about the flow pipe. The vent can be moved when you put the new plan into the cylinder cupboard, in behind the new pump position.

I would go for an S plan rather than a Y plan. Easier to wire, more reliable and should sort out any reverse circulation issues.

Sam

 

[Gerontius]

Sorry - thought I had posted reply but seemed not to get through. Thanks for advice re S plan, which I just checked on Honeywell.

But as far as location is concerned, boiler and cylinder will remain much where they are - so there will still be a 5 metre run of pipe which is only a couple of degrees off horizontal - above the boiler is only a flat roof. Can I continue with this layout? Would a heating engineer agree to do the work on it, as it is?

 

[heatingman]

check with pott/baxi, I think they still permit install with pump on return. wireless danfoss cylinder stat and pump and motorised valves on return. Best to go with 2 port valves.

 

[Gerontius]

Thanks heatingman, you've revived some optimism! Just found a pdf of the Potterton install and it states 'pump may be fitted on either the flow or return...'. Now my worry is the long horizontal run on the flow/vent..... I know it has been alright for 30 years, serving three boilers. But can I continue with it. Knowledge is a dangerous thing! I've lived with it for 20 years without a qualm!