Boiler problem or pipework problem? Help

[CAS50]

Looking for help and am really getting desperate now.

I have had a problem with my heating system for a few years not and it is gradually getting worse. The top of radiators are hot and the bottom is cold resulting in the rooms not being adequately heating in the cold months.

Boiler, rads and all pipework is 6yrs old. Boiler is a Vokera Linea Max with 22m pipework throughout. I’ve had the inhibitor in it since new.

Recently I have treated several times with X400 and flushed but it’s made no difference. I replaced all downstairs return pipework and installed a new radiator in the living room. It immediately got the same problem. I have had folk in to power flush the system and they said no blockages or restrictions in flow or significant particles found.

I have had the manufacturer from the boiler out and they sat the boiler is working fine problem is a blockage in the pipes.

The burner comes on and heats the water until it reaches cut-off when the flow temp reaches 82degrees. The burner then stays off for three mins. Temp gauge is then down at around 43 degrees. I therefore assume this is the return temperature.( the boiler temp gauge is on the flow pipe) When the boiler comes on the temp ramps up to 82 where it cuts off again. This repeats constantly and because the boiler does not stay on for long each time (1-3mins) the system and rooms do not heat properly. Even with the boiler at max the return temp only gets to 43. I have changed the pump for a Grundfos UPS15-60 (recommended replacement by Vokera) and this made no difference.

I have fitted a flow meter and now know that the flow around the system is 500l/h. There is a radiator about 1m from the boiler and the flow rate does not change if this rad is open or closed.

Help can someone give me an indication of where they think the problem lies and what I should do next.

Thanks.

 

[powerflushingpro]

If the water is moving but the radiators is not all the way hot, it sounds like you need a power flush asap. Problem builds up as the sludge forms and gets more and more.

 

[CAS50]

I have had this done and didn't make any difference. I also installed a brand new radiator when i replaced the return pipework and this had the same problem immediately even although it defo had no sludge in it.

 

[danplumb]

Have you simply tried balancing the system properly ?

 

[CAS50]

I have isolated all rads but one and still cannot get the return temp up enough to 20 degrees below the feed.

 

[Steambod]

500 l/h??? Works out at about 6kW. Sounds a bit low to me. Is the diverter valve inside the boiler working? (I believe you said Linea Max, combi boiler?). Download the manual http://www.vokera.co.uk/trade-professionals/manuals-literature/ and go through the section on operation (section 2). That should give you an idea where the trouble might lie. I'd be pretty surprised if sludge was the problem after only 6 years especially as you've got inhibitor etc in already and reckon the trouble is internal to the boiler.

 

[CAS50]

It has recently had a new diverter valve. Does the flow seem rather low to you. I was thinking of temporarily connecting some new pipework to another single radiator to check the flow rate and flow/return temps.

This would then see if the problem was the boiler of the pipes.

Does that sound reasonable?

Vokera think it is a system problem and will not look at the boiler further. (Pipework is not covered under my Domestic & General policy)

I just need to find the problem and fix it. On the plus side my gas bill was much lower this winter albeit the house was cold and i had portable gas heaters around!

 

[Gas2Air]

You have no idea what you are doing. You are guessing. You have fitted the pipework, you have balanced the system according to the boiler size. you should know the answer? Oh no, well why not bite the bullet. Probably get someone who knows and rip out your work and start over?

 

[UpgradeME]

Boiler, rads and all pipework is 6yrs old. Boiler is a Vokera Linea Max with 22m pipework throughout. I’ve had the inhibitor in it since new.

How many rads and what kW output? (Use Stelrads site to check) Are they all connected with 22mm tails or something else? Who designed / fitted the system originally? Did they heat correctly then?

Temp gauge is then down at around 43 degrees. I therefore assume this is the return temperature.( the boiler temp gauge is on the flow pipe)

The gauge will be showing the flow pipe temperature at that point in time, which isn't the same as return temp when operating. You will need a thermostat to check pipe temps whilst the boiler is operating if you want to check the delta between flow/return.

I have changed the pump for a Grundfos UPS15-60 (recommended replacement by Vokera) and this made no difference.

I have fitted a flow meter and now know that the flow around the system is 500l/h.

I'm not a pro so don't have any experience with this boiler, however, having just been taught on here about flow rates, power and delta temperatures in my own thread, my instinct/guess is that the flow rate is too low, possibly caused by having oversized pipes. (not enough info provided to say for sure, so pure guess there)

There is a radiator about 1m from the boiler and the flow rate does not change if this rad is open or closed.

Try closing off all the rad's appart from the closest one to the pump, does this rad then warm up along the bottom? Can you check the flow rate when only one rad is open? If so, try opening up a few more and see how it affects the flow / radiator output. At what flow rate do they stop working correctly?

 

[Agile]

One of your problems is that your boiler heat output is set too high causing it to turn off and then go into anti cycle mode. So the burner is only firing for 1-2 min every 5-6 min.

I dont know if there is a CH power output setting on your boiler. Check the instructions for this. It may be there but not mentioned!.

When that has been set you need to have the boiler's gas valve settings checked by a competent person. My fear is the minimum is too high.

Nor am I sure your system is properly balanced based on what you have said. You need a contact thermometer and to measure the flow and return temperature at each rad.

Whilst you say its been power flushed, to me that proves nothing. There are many people who connect a power flush pump, read a newspaper for two hours and then disconnect it. Power flushing, done properly, is quite energetic and I prefer to have an assistant to help me although I do agree that its very good exercise!

Tony Glazier

 

[UpgradeME]

One of your problems is that your boiler heat output is set too high causing it to turn off and then go into anti cycle mode. So the burner is only firing for 1-2 min every 5-6 min.

I dont know if there is a CH power output setting on your boiler. Check the instructions for this. It may be there but not mentioned!.

Looking through the MI there is a customer dial for CH temperature but the power output on this model is 'self modulating', as follows:-

An automatic range-rating facility is incorporated in the boiler for the central heating system in conjunction with the electronic burner modulation.

The burner ignition is checked by the electronic circuitry to ensure correct ignition of the burner. Once successful ignition has been achieved, the electronic circuitry increases the gas rate to 75% for a period of 15 minutes.
2.2.3 As water temperature increases this is sensed by the temperature sensor on the flow pipe which modulates the burner to match the heat output to the heat requirement of the system.
2.2.4 Depending on the load, either a) the water temperature will continue to rise and the burner will continue to modulate down until the maximum setting is reached at which point the burner is switched off, or b) the water temperature will fall and the burner will return to a higher output to match the demand.

6.7.8 Setting the Maximum Rate for Central Heating
The maximum heat input for the central heating mode is not adjustable.

As the max output is 29kW, for the first 15 minutes would it be running at 21.75kW (75% of 29kW) which may be too much for the system causing the cycling?

 

[Agile]

He has not told us the size and type of house. A 3-bed semi needs about 10-12 kW and the boiler should be set for that power.

Putting 21 kW into the system will cause it to rapidly reach the set temperature and as the modulation range will not be wide enough it will go off for the anti cycle delay time. Some are adjustable but many are not. The minimum power is set by engineer adjustments on the gas valve.

Tony

 

[CAS50]

Thanks Agile

My house is four bedroom detached property with high ceilings and single glazed windows. Its very drafty and a b*gger to heat.

I have 17 radiators and a towel radiator.

I had been thinking that there may have been a problem with the self-modulation on the gas supply to the burner but Vokera though it was just poor flow meant it could not modulate enough without overheating.

The power flush was done by a company i trust. Two of them spent 7hours doing it and constantly running over the house switching of and connteding radiators.

Do you think 500l/hr is too low?

 

[Agile]

We do not normally measure CH flow rates although they could be calculated from the heat input if anyone was that bothered. It does sound a little low to me but thats not based on any measurement experience. We work on what we can measure which is the temperature differentials.

Your immediate problem is the boiler is only firing for 1-2min every 5-6min. Even at 21 kW thats only equivalent to 4-7 kW which is far too low.

For me to comment further I would want to know the min power output of your boiler.

Tony

 

[CAS50]

Central heating output of the boiler is from 9.9 - 28.0kW
Designed temp rise 20 degrees
Minimum flow rate for heating is 360 l/hr