Boliermate 2000 Potterton Suprima 40L anti cycle

[Trumpet]

Hi all
I'm looking for some advice (aren't we all!) with regards my heating issue.

The problem is the store (Boliermate 2000) never gets upto temp because the boiler (Potterton Suprima 40l) goes into anti cycle mode believing the boiler temp control is satisfied. However the store is not satisfied and so continuously calls for heat. The end result being short 30 second burns with 5 minute anti-cycle waits inbetween.

Fixes tried so far
-------------------
Boiler temp control set to max
Boiler serviced - thermistor replaced
Store temp replaced - all sensors working
Pumps removed circulation checked

I know the boiler is capable of heating the water to temperature hot enough to satisfy the store (74-77C) as the temp of the water being delivered to store has been measured as 79C. It just doesn't seem able to deliver this amount of heat in sufficient quantity to heat the entire volume of water stored.

Should the bolier switch off immediatley when 79C is reached or should it deliver this heat for a few minutes?

Any suggestions and advice welcome

 

[BigBurner]

If the store is calling for the boiler and it does not heat up the store, and there are no circulation problems, the problem is the boilers controls.

The boiler should heat the 2000 up no problem.

 

[baxpoti]

Sludge jumps to mind.

 

[BigBurner]

Sludge jumps to mind.

He said it was clear. A Mangnaclean on the return to store from the rads would be wise, if it is direct heating of course - well essential really. The boiler could be full of sludge though.

 

[ChrisR]

The boiler will turn off when the max temp is reached. 79 is about where that is. It'll turn back on when the temperature drops - there will be some hysteresis (play) in the control.

I can't rmember whether the anti-cycling inhibition is invoked when the boiler's own thermostat tells it to fire again. I think it only applies to the external (2000) call for heat AFTER it has stopped calling for heat.

What you need to measure are the return temp from the 2000 when the flow's at 79, and the flow /return temps when the boiler cuts back in again.
How long does it take from cold fror the store to get up to the point where the boiler cuts out? The capacity of the 2000 would give a guide as to how long that should take if circulation is OK.

What do you mean by "circulation checked"? SLudge springs to mind - it's common with boilermates.
It's pretty difficult to know what the circulation rate is, and whether it's impeded by a knackered pump or blocked system. It's usually simple enough to try a new pump, unless grotty valves have been used.

Try letting some water out of the drain cock lower right. Bet it's black!

 

[Trumpet]

Wow, quick response! Thanks guys.

The store was drained to replace the valves above and below the pumps as these were leaking when the system got cold (as I don't leave it on while it has this problem) and the water was clear. Even though the pumps sounded fine the boiler/CH pumps were swapped over and the heating engineer blew down the pipes to see if he could feel blockage/resistance (?? how acurate is this method ??)

Temperatures were recorded at the store during the short 30 second burn phase as 72C to boiler and reaching 79C on the return. It's this 30 second burn I don't understand before the boiler anti-cycles - the store holds 125 litres, you'd have to deliver a volume of water at 79C over a period of time before the whole store gets up to temp.

 

[jackthom]

Is the boiler cycling happening right from when the store is cold or only as it gets close to its target temperature?

If it's only when in the final stages of heating up the store, I'd say the boiler doesn't have a high enough maximum flow temperature to finish the job properly. The manual recommends at least 80C flow and the more the better.

Check the boiler thermostat - this should be
set at maximum.
Check that the boiler flow temperature before
it is switched off by its own internal thermostat
or the store sensor is adequate - it should not
be less than 80°C.

I wonder if the boiler manufacturer could suggest how to safely increase this a little.

 

[BigBurner]

Is the boiler cycling happening right from when the store is cold or only as it gets close to its target temperature?

If it's only when in the final stages of heating up the store, I'd say the boiler doesn't have a high enough maximum flow temperature to finish the job properly. The manual recommends at least 80C flow and the more the better.

Check the boiler thermostat - this should be
set at maximum.
Check that the boiler flow temperature before
it is switched off by its own internal thermostat
or the store sensor is adequate - it should not
be less than 80°C.

The store is self adaptive. It learns about the boiler. It will go as low as 75C.

Check to see if the boiler's heat exchanger is not blocked.

 

[BigBurner]

Once you have solved the cycling problem, I would do the following:

1) Fit a Magnaclean filter on the CH return loop to the Boilemate.
2) Make sure you have enough inhibitor in the system - minimum 2 cans of X-100.

You can improve the system further.

1) Replace the CH pump (have this as a spare for the others, so no waste) with a Grundfos Alpha or Wilo Smart pump (£45 on s/fix). Fit a full bore valves either side of the Magnaclean.
2) Link out the room stat terminals and remove any wall room stat.
3) Fit TRVs on all rads.

Comfort conditions, economy and pump noise levels will be improved.

So for under £180 you can give top class protection to the system and gives superior comfort conditions in the house...and less pump noises.

 

[Trumpet]

jackthom wrote:
Is the boiler cycling happening right from when the store is cold or only as it gets close to its target temperature?

If it's only when in the final stages of heating up the store, I'd say the boiler doesn't have a high enough maximum flow temperature to finish the job properly. The manual recommends at least 80C flow and the more the better.
Quote:


Check the boiler thermostat - this should be
set at maximum.
Check that the boiler flow temperature before
it is switched off by its own internal thermostat
or the store sensor is adequate - it should not
be less than 80°C.

The cycling happens when the store reaches about 73C and as BigBurner says the store is self adaptive to the boiler output when setting the store temp range, this it sets at 74C to 77C. This matches my neighbours setting who have the exact (albeit working) system.

As an experiment I removed the boiler thermistor from the flow to see what would happen. The store reached 77C but I could hear the water boiling in the heat exchanger so I swutched it off. Thought the overheat stat would have kicked in to prevent this!

Is it posible to drain just the boiler heat exchanger without draining the whole system? I'd like to remove it and check for sludge.