Questions about CH system upgrade

[benawhile]

I need to replace a Glow Worm Fuel Saver B that heats my small 3 bed terrace house, and add a bathroom radiator. I am also interested in converting from an open vent system to a sealed system, although I definitely do not want a combi.

I would like to use an Intergas boiler, as I have heard about them on this forum.
My second choice would be Vaillant
Apart from that I wish to keep costs as low as possible and hope I will be able to retain at least some of the present control system and plumbing.
I wish to keep the boiler in the bathroom upstairs not least as it is next to the internal soil stack and condensate drainage would be simple.

My current system is fully pumped with a 3 port 3 position motorised valve, albeit now too stiff for the Duval motor to turn it. The positions are hw only, hw and ch, ch only
The hot water cylinder is in the upstairs airing cupboard in middle of house, with controls, 3 port valve and pump. I cannot see any bypass anywhere.
There are 5 radiators in the whole house. Each has a LSV and a wheel valve.
No TRVs. The room stat is downstairs.
The present control is a Potterton EP2000 via a Satchwell 437-2-802 wiring centre.
Recently fitted Grundfos 15-50 130 Selectric pump.
Downstairs rads are drop fed, no piping under the ground floor. I had thought about separate zoning for the bedroom circuit but all rads are currently mixed in the same circuit under the upstairs floorboards.
The narrowest piping is ½ inch.
I used an online heat loss calculator which came up with 4.18 KW for the house.

Could you advise if this is an S plan or Y plan? I think it is a Y plan.

I have contacted Intergas and they advise that their HRE 18 SB would be suitable, but if necessary I can stay with an open vent. The SB is downgradable to OV. I would like the Robokit with a view to putting the expansion in the airing cupboard.
I have no pump run on system yet but from what I can make out I can retain the Potterton controls as the pump run-on is controlled from the Intergas Boiler, I want to simply upgrade from the EP 2000 to the 6000. Is this correct?

I want to add a bathroom towel rail but not as a bypass circuit. I would want to turn it off in very hot weather. Can I have a wheel valve one end and TRV on the other?
I have read about Magna clean, Combi mate, Hydroflow hs 38 and Sesi Salamander but not sure what I need. My local water is hard, (Basingstoke)
I want the Magna clean but have to choose between Professional, Micro and Twin Tech models. I want the best and am prepared to have a Combimate or Sesi as well but don’t know if there is a need for this, in any case I want something to stop the hot water circuit scaling up as well. Can you advise on this? I will be having a power flush.

Would you advise replumbing from one three port valve to two separate two port valves, and would this mean getting a new control unit or wiring centre?

A local heating engineer advised that TRVs are not strictly required and the priority is to get the balancing correct. One thermostat and the rest TRV seems like a compromise, on an academic point only, would the best system be to have a separate MV for each rad and a thermostat in each room?

Many thanks for reading all this.

[Atticus Finch]

I am also interested in converting from an open vent system to a sealed system

The danger with a system boiler in an existing system is that the higher pressure at which the sealed system works may expose weaknesses in the pipes and radiators.

I wish to keep costs as low as possible and hope I will be able to retain at least some of the present control system and plumbing.

You need controls which will allow the system to operate at its most efficient

I wish to keep the boiler in the bathroom upstairs not least as it is next to the internal soil stack and condensate drainage would be simple.

That shouldn't be a problem.

I cannot see any bypass anywhere.

Very unlikely that there will be a bypass on a system that old.

No TRVs.

Although not compulsory when fitting a replacement boiler, the official advice is that, as the system has been drained to fit the new boiler, it is a sensible time to fit TRVs.

Recently fitted Grundfos 15-50 130 Selectric pump.

Seems a pity to waste that pump by fitting a system boiler.

I had thought about separate zoning for the bedroom circuit but all rads are currently mixed in the same circuit under the upstairs floorboards.

Zoning in a house as small as yours is a waste of money.

I used an online heat loss calculator which came up with 4.18 KW for the house.

Then you need a small boiler. The Intergas only modulates down to 5.6kW, so it will spend all its time in on/off mode, which is less efficient. Unfortunately there are very few boilers which modulate much below 5kW, which is an oversight by boiler manufacturers as there are many houses which require a boiler that small.

I think it is a Y plan.

That's right

I have contacted Intergas and they advise that their HRE 18 SB would be suitable

Would you expect them to say otherwise?

I have no pump run on system yet but from what I can make out I can retain the Potterton controls as the pump run-on is controlled from the Intergas Boiler

That's correct - pump overrun is boiler controlled. That's no problem if you have a system boiler as the pump is in the boiler. But if you have an open vent boiler you will have to make sure the cable from boiler to the wiring centre has sufficient cores to control the pump in the airing cupboard

I want to simply upgrade from the EP 2000 to the 6000. Is this correct?

There are much better controls now available.

I want to add a bathroom towel rail but not as a bypass circuit. I would want to turn it off in very hot weather.

Will you want the towel to work in the summer, when the heating is off?

Would you advise replumbing from one three port valve to two separate two port valves

No

A local heating engineer advised that TRVs are not strictly required and the priority is to get the balancing correct.

See above. Balancing is important.

One thermostat and the rest TRV seems like a compromise, on an academic point only, would the best system be to have a separate MV for each rad and a thermostat in each room?

It is a compromise but, provided it is correctly adjusted, can be a very successful one. Separate MVs and thermostats is overkill.

[benawhile]

Thank you for this.

In order, I hope:

Am aware of a certain risk in going up to a system boiler, but not a clue what mightwill go wrong in my case. Distinct advantage in dispensing with loft F and E tank isthat I have a small loft and elaborate carpentry and replumbing required as current F & E squats on top of HW header with no overflow except by dribbling over rim of F & E in to HW expansion! I also want to leave room to raise the hw tank to improve pressure in the shower.

Having difficulty looking for small boilers, SEDBUK site only gives cost figure for typical size house, so every boiler listed costs 262 to 260 p a.! Could you suggest where to look and what figure to look for? I need to know how much heat is wasted by a boiler rated, say, 1kw too high. The theory is explained here
http://www.idhee.org.uk/calculator.html
but it seems to be out of date, referring to cooling air coming through the base of the boiler, and boiler firing when no heat is needed, which seems to conflict with interlock practice.

I would want the towel to work when the central heat is off, i have seen intructions for plumbing it so that it receives water from hw circuit as well as ch.

In what way can better controls improve on the EP 6000?

[Atticus Finch]

Am aware of a certain risk in going up to a system boiler, but not a clue what might/will go wrong in my case. Distinct advantage in dispensing with loft F and E tank is that I have a small loft and elaborate carpentry and replumbing required as current F & E squats on top of HW header with no overflow except by dribbling over rim of F & E in to HW expansion! I also want to leave room to raise the hw tank to improve pressure in the shower.

The biggest problem will be leaks from joints or pinholes in radiators which have corroded from the inside.

Presumably you mean raising the cold water storage tank to improve shower pressure.

Having difficulty looking for small boilers

If you mean low output boiler, join the club! Baxi have recently introduced a new range of boilers which have very low outputs, including a system boiler which modulates between 2kW and 12kW.

http://www.baxi.co.uk/docs/Megaflo-consumer_brochure_8pp_%28low_res%29.pdf

I need to know how much heat is wasted by a boiler rated, say, 1kw too high.

Having a boiler which produces more heat should not be a problem as it will automatically modulate down to the required output. It does this by measuring the flow temperature and adjusting the output to maintain the required temperature - like easing back on the throttle of a car when the required speed has been reached.

The problem is at the bottom end, for example in the spring when outside temperatures are higher, so less heat is required, when the boiler cannot modulate low enough to maintain the desired water temperature. In these circumstances, the boiler will light modulate to its lowest limit and then, finding that the water temperature continues to rise, shut off until the water temperature has dropped below the set value. It then relights and the cycle start again. This can be very inefficient, getting worse as the on time becomes a smaller proportion of the on/off cycle.

I would want the towel to work when the central heat is off, i have seen instructions for plumbing it so that it receives water from hw circuit as well as ch.

Don't forget that the towel rail will only heat up when the hot water is being heated - which may not be when you actually want the towel to be warm!

In what way can better controls improve on the EP 6000?

The 6000 is just a time control, which means that, unless you are vigilant and alter the morning ON time according to the weather, before you go to bed, on many days of the year the heating will be coming on much too early, wasting gas. If you have a programmable thermostat, there are models available which will do this automatically. You just set the time when you want the house to be warm, i.e when you get up, and the prog-stat automatically adjust the on time according to how much the temperature has dropped overnight and how long it takes to get up to temperature. (It will take a few days to learn this.)

Modern digital thermostats control the room temperature more accurately and can prevent overshoot (room temperature rising too far above set value) and undershoot (falling too far below set value).

As you are not fitting a combi boiler, you need to be able to control HW times as well as CH times. There are two ways of doing this: A programmable stat (e.g Honeywell CM900 series) and a separate HW timer (e.g Honeywell ST9100A or C); or, a combined CH/HW timer with wireless connected thermostat (e.g Honeywell Sundial RF² Pack 2.