Heating System, setup advice please

[GICarey]

Hi Folks,

Apologies, long post, in an attempt to provide as much information as possible up front.

I recently moved house and have inherited a heating system which appears to have been reasonably well installed (by British Gas), but has suffered, maintenance wise in the last few years.

EDIT TO ADD: House is old (18th C 9" solid N-facing front wall, 1950s (cavity) everywhere else), with insulation crying out to be upgrades.

EDIT AGAIN TO ADD: Boiler is a BG 330+ set at 28Kw (Believe this is a rebadged GlowWorm Flexicom HX with a posh display).

We had the boiler serviced prior to moving in (a family member was present, I was not), and through the winter I have performed a few 'remedial' tasks (e.g. replacing broken Zone valve, repeated cleaning of magnaclean to try to degunge system somewhat, and replacement of Kitchen radiator) to keep it ticking over / us warm until I can get the time to drain down, and treat with chemicals, etc to 'clean it up' properly (to be honest, rads are old inefficient sort, so may swap them all out in one go at that time).

The most recent remedial task necessary was this past weekend. Replacing the BG Multihead G pump (with a Grundfos UPS2), as had noticed the old pump was incredibly noisy, and only really worked on highest setting, and was not always starting when receiving power (causing boiler to enter into a 'dry' fail mode, requiring reset). Removal of pump head showed the expected rust & gunge build up.

UPS2 is now fitted, incredibly quiet in comparison, and has had a number of knock-on effects to the rest of the system, as follows:

* Boiler 'approach to heating water' appears to have changed, with longer periods of it running 'flat out' before stepping down to 1/3-1/2 power to maintain temperature.
* Radiators all generally hotter, esp. those at end of circuit which had been difficult to get hot previously.
* Noticing a significant increase in noise from the TacoSetter set as bypass for the system (i.e. when both valves closed in overrun).

Here's a diagram of what the system layout looks like:

Heating System Diagram

• GICarey
• 17 Feb 2014
• 1

(I failed to include a return from the radiators, but it comes up from the floor before being joined by H/W return, TacoSetter return and before flowing into the MagnaClean)

And so, finally, to questions:

1] Any advice on correct pump setting for the system I have? Or trial-and-error approach? Doesn't seem to syphon or pump out anything into/from header tank on any setting.

2] It would appear I will need to go through the process of balancing the radiators again - correct?
2a] Assuming yes, aiming for 12ish degree drop across each rad?
2b] What overall drop should I expect across the boiler flow/return?
2c] If drop across the boiler flow/return is smaller than target, do I reduce pump speed and start the balancing process again?

3] Noise from the TacoSetter is presumably due to increased flow through it when it overrun (new pump dishing out a lot more power than old).
3a] Adjustment of TacoSetter presumably needs to be a part of the balancing process? It has letters A through G repeated around the screw, do these serve any useful purpose in the setting process? Or is it simply a gate valve with a flow rate meter built in?
3b] the flow-rate meter on the TacoSetter is rather 'gunged up', what should I be expecting to see in there behind all the gunge? Or is this an indication I should ignore the reading.
3c] What kind of flow-rate should I be expecting to set here when in overrun mode?

Many, many thanks in advance for taking the time to look and respond.

Regards,

Gavin.

 

[Gas2Air]

Why are you obsessed with the bypass? You're gaining nothing from your post. Everything is working isn't it? UPs2 can manage their load.

 

[GICarey]

Bypass - I have reason to believe it's been heavily fiddled with by previous owner (screw somewhat chewed up), and was broadly open when we moved in. This, I think, means a lot of hot-water being dumped into the return to the boiler, reducing the differential and thus the overall efficiency of the system (boiler reading 80-100 (I presume Kw) burned per week-day (morning/evening heating) and 150-180ish per weekend day (all day heating)) so would like to keep costs down.

 

[Gas2Air]

Bypass - I have reason to believe it's been heavily fiddled with by previous owner (screw somewhat chewed up), and was broadly open when we moved in. This, I think, means a lot of hot-water being dumped into the return to the boiler, reducing the differential and thus the overall efficiency of the system (boiler reading 80-100 (I presume Kw) burned per week-day (morning/evening heating) and 150-180ish per weekend day (all day heating)) so would like to keep costs down.

Take it out then, fit a gate valve, turn it down until your costs come down.

 

[GICarey]

Is that not what a TacoNova Setter is, a gate valve with a flow rate meter on it? I assumed so in the OP, along with enquiring about minimum flow rate for my particular boiler (my understanding is that closing the gate valve too much would mean too low a flow through the boiler when in overrun, risking damage to boiler?), thus, on a fixed-speed pump I'm assuming the game is to find the correct balance between bypass flow and return temp?

 

[Gas2Air]

Jesus. On a correctly fitted system and bypass with 2x 2ports, what the eff are you going to save on gas?

 

[GICarey]

Jesus. On a correctly fitted system and bypass with 2x 2ports, what the eff are you going to save on gas?

Honestly, I don't know (which is why I'm posting here asking questions of the experts), the answer may be minimal, but one assumes, however, there's a reason for fitting something adjustable between flow and return, vs a straight pipe (all be it smaller bore than the 22mm)? I thought I'd read somewhere regarding a reduction in efficiency without sufficient differential between flow and return?

Having tracked down the install/service manual for the boiler http://www.glow-worm.co.uk/stepone/data/downloads_sd/df/00/00/flexicom-hx-instn.pdf I can see that:

- I should be looking for a minimum 20l/min through the bypass when in overrun mode.
- It specifies a maximum differential of 20oC between flow and return, though doesn't mention how efficiency changes as this differential varies - maybe it doesn't and thus you're entirely correct.[/url]

 

[GICarey]

Ah, further reading suggests I need to aim for a return temperature below a certain level (maybe 54oC) to gain the efficiency of condensing, is that correct?

 

[D_Hailsham]

What setting is the pump on?

Re-balancing is probably a good idea, but you should balance for a 20C drop across the rads, which is what the boiler is expecting.

Quick Balance Method

The Documents written by Paul Carne from Grundfos on bypass setting etc. are very helpful.

PS

30kW is a large boiler. Do you have a very large house?

It might be worth using the Whole House Boiler Size Calculator to find out what size boiler you really need. The output of your boiler can be reduced if necessary.

 

[GICarey]

Hi,

30kW is a large boiler. Do you have a very large house?

House is reasonably large, tho not huge, however it needs some serious improvement on the insulation front, however, front wall is single skin 9" brickwork about 15m long over two stories, with 9 1.4m tall by 1m wide draughty single glazed windows. Remainder of walls are 1950s unfilled cavity, remainder of windows all single glazed and glass covers most of the south side of each room. Roof insulation needs a serious overhaul.

Calculator (without water requirement) gave me a requirement of 24Kw with standard window sizes, and assuming unfilled cavity. So, with boiler rated at 28Kw we are over-specced, but not hugely so.

Once we double-glaze, fill cavities, sort the roof insulation out and perhaps stud-and-insulate the north-facing front-wall, we will be heavily over-specced on the boiler front, but... the house is a projoect, so much of that won't come for a while yet.

What setting is the pump on?

Once I noticed how much crap was being pulled out of the system to the Magnaclean with the new pump in (old one must have been truly awful), I have left it on III for a few days, cleaning the Magnaclean sheathe every half-day or so. This morning was the first time it hasn't been totally caked (rings of sludge rather than a solid coating). I'll probably leave it at III through the rest of this week and keep on with the cleaning process until it's looking more healthy, then dial it back as part of the balancing process.

 

[D_Hailsham]

Calculator (without water requirement) gave me a requirement of 24Kw with standard window sizes, and assuming unfilled cavity. So, with boiler rated at 28Kw we are over-specced, but not hugely so.

As I said in my last reply, you can reduce the output of the boiler; it's parameter d0.

Once we double-glaze ... we will be heavily over-specced on the boiler front.

Did you use the calculator to estimate the new requirement?

I'll probably leave it at III ... then dial it back as part of the balancing process.

Balancing must be done with the pump on a fixed speed.

Condensing does not start until the return temperature is below 55C. The lower the temperature, the more condensate produced. Your boiler is designed for a 20C temperature difference; so 75C flow, 55C return. If you balance the rads for this difference they will produce about 15% less heat, so you need to install rads which are 20% larger.

Bypass setting
The Taco Setter is, as you guessed just a gate valve with a flow meter.

A flow through the boiler of 22l/min is only required at max output; it ensures that the differential does not exceed 20C. If the same flow rate is maintained at minimum output (9.3kW) the differential would be only 6.2C. To maintain a 20C differential at min output will require a flow of 6.7l/min.

I'm not convinced that you need to maintain the same flow rate all the time, even when the boiler is turned off, i.e in overrun.

 

[GICarey]

D_Hailsham, thanks for your reply, apologies for nearly a month in coming back. Household taken by various bugs!

Parameter d0 for adjusting down the boiler maximum output. Got it. Is it worth adjusting, however? The boiler adjusts its fire up and down based on need, so presume it would only run on say 2/3 rated max, vs running to max at a setting of 18kw? Or, does rating down carry some innate advantage (perhaps self rating then happens in smaller increments?)

Yes, used the calculator for various scenarious to confirm what things would look like once the glazing is upgraded, insulation in place etc (those numbers really help you prioritise that work!)

As for radiator size. Again, thanks, that's useful. In all honesty, the ancient panel rads fitted in most of the house are really not up to the job of heating the place, expect they'll all be swapped out over the coming year or so as we do work.

For flow rate, my assumption was that, when in overrun mode, the purpose of the flow is to cool the aluminium element, to prevent overheating & warping? So, would agree, maintaining a high flow rate during that period doesn't seem overly vital,as - given the short distance the water will cover when pumped around this loop - there's only so much temperature it's going to pick up and carry off with it anyway, lower flow rate should mean cooler water coming back into the boiler?[/i]