Not Getting Hot Enough!

[Nelly B]

Hi there.
I have a Greenstar 24RI boiler and a gravity system with a hot water tank on the ground floor. I have an extended chalet bungalow, 7 radiators downstairs and 5 upstairs all with TRVs. Boiler is 7 years old and just had a new pump as old one was very noisy. Struggling to get house up to temperature. Water OK.

Boiler set to around 75% heat. Radiator temperatures range from 38 to 53. Boiler out temp is 59, return is 37. Room tends to hover around 19 with thermostat set to 22. Radiator balancing has been carried out.

My question is this. I have noticed that typically the boiler fires for around 1.5 minutes and then is off for around 3 minutes. This cycle is continuous. I read that the boiler may by 'short cycling' so I would welcome your views whether that is correct and any possible solutions.

Thanks, Nelly

 

[Mottie]

We're currently staying in a rented cottage with the same boiler except it’s a combi. It just wasn’t getting the place warm. Looking at the controls, the owner has left a note on the flap saying 'do not adjust the settings'. The heating flow temperature was set at 60°. I set it at 70°. That did the trick.

 

[CountryFan]

What pump was fitted and if speed control, what speed is it on? Might be worth checking the motorised valve too.

 

[Nelly B]

Thanks guys. I have tried putting the heating control to max. This helps in that the radiators now range from 46 to 56 (with a bit more balancing) but not as hot as they should be I think.

The pump is a brand new Grundfos UPS4 Go. The motorised valve seems to be working correctly.

I would still like to know if any boiler experts out there think the short cycling I originally described is correct operation? I would of thought the boiler would stay on for much longer periods in order to meet the room thermostat demand.

 

[Fred Blogs]

I have a Greenstar R21 0r 24 ( no number on the case) Condenser boiler and mine doesn't cycle on and off every couple of minutes. In fact mine appears to be on all the time, it is in my garage so I don't watch it that much, although I suppose it will turn off when it reaches temperature. I have the boiler thermostat set about three quarters of the way round.

 

[Madrab]

Has this only started since the new pump went in?

No - the boiler shouldn't be short cycling, with all 12 of the rads (average sizes?) calling for heat then that boiler should happily modulate down to around 7Kw.

If it's short cycling then it means the boiler is reaching max set temp and shutting down as it cant move the heat out quickly enough.

 

[Nelly B]

Thanks again guys. I believe the radiators are average size although there are 2 doubles. I don't think the pump replacement made any difference apart from being much quieter. However I did not notice what the boiler was doing before we changed it.

If the boiler cannot move the heat, could that be due to a blockage or other reasons?

 

[Nelly B]

Further to my last post I monitored the boiler during Monday to see if there is any pattern in what it is doing. Boiler control set at 75%.
The heating is set to come on from 6am to 11pm. Demand is continuous as the room thermostat never reaches temperature. The water comes on from 6 to 8am, 1 to 2pm and 5 until 6pm.

The following observations were made:

From 6 to 8am: Not monitoring at this time but noticed that the radiators stayed luke warm.

8am: Boiler fired continuously for 1.75 hours. Maybe coinciding with water going OFF.

9.45am Short Cycling (on for around 1.5 mins off for 3 mins) for 1.25 hours. The 3 minutes is very consistent.

11am Boiler on continuously for about 1 hour.

11.50am Short Cycling for 1 hour 10 mins.

1pm Boiler comes on for 16 minutes. Same time as Water goes ON.

1.16pm Short Cycling for 44 mins.

2pm Boiler on continuously for 1 hour. Same time as water is OFF.

3pm Short Cycling for 2 hours.

5pm Boiler stays firing for 37 minutes. Same time as water goes ON.

5.37pm Short Cycling

6pm Boiler stays on for 1 hour. Same time as water goes OFF.

7.20pm I decided to check the 3-way valve. Heating OFF. Water switched ON. Goes into Short Cycling

7.35pm Water OFF and Heating back ON. Boiler fires continuously for about 1 hour.

8.30pm Short Cycling until around 9.30pm. Boiler then goes ON continuously but I don’t know for how long.

10pm Monitoring stopped.

So although the boiler does fire continuously for some long periods the Short Cycling prevents the room temperature building up. The action of the water going On and OFF does seem to influence matters.
It looks like the boiler is not functioning correctly, but is that the boiler itself not setup properly or defective, or due to external factors.

I welcome your views.

 

[Madrab]

Has this only started since the new pump went in?

??

What size is the pipework? 22mm > 15mm or 22mm>10mm

Output tempt on the flow pipe under the boiler if boiler on max? How long is the run to the HW cylinder?

Certainly sounds like a circulation issue.

 

[Nelly B]

Thanks Madrab.
Downstairs (7 rads) is 22mm. Upstairs (5 rads) is 15mm as this was done as a chalet bungalow extension.
Flow pipe temp is around 64 max. From boiler in kitchen the pipe goes to the 3 way valve in the airing cupboard which is downstairs about 7m away. Hot water cylinder is about 0.5m from the valve also in the airing cupboard. From there the pipes go into the floor for downstairs rads and upstairs (in 15mm).

 

[ericmark]

Demand is continuous as the room thermostat never reaches temperature.

This is what I thought, the thermostat it seems is designed to stop hysteresis, and as it approached the set point, it starts a mark/space ratio so it will not overshoot.

This house fitted a second thermostat in parallel to the first in living room, first one in hall, it should have not made a difference, but it did, living room now lovely and warm.

 

[Nelly B]

No I don’t think so ericmark. I have a Salus IT500 smart thermostat and the room never gets anywhere near the set point as I set it high to ensure the boiler keeps firing if it can, I.e to investigate what is happening. Temperature does not generally get above 19.

 

[Madrab]

Has this only started since the new pump went in?

??

 

[Nelly B]

No afraid not. Pump was changed to try to fix the problem. It was quite old and becoming very noisy anyway.

 

[desktop987456]

Certainly sounds like a circulation issue.

check trvs, I have a setup similar to yours, OV boiler 13kw feeding 7kw load for space heating, nice temperature difference between flow and return on boiler loop. The boiler short cycled and my gas usage had gone up. I tried different pump speeds but it turned out to be blockage in one of the least used radiator in a bathroom due to circulation problem as Madrab has identified above because as soon as I fixed the blockage in that radiator the short cycling stopped and it operated fine ever since. Check all trvs and rads if all of them are heating at the same time.