C/H but no H/W

[Connor]

Any help would be greatly appreciated.

I have an indirect C/H system with two 2way valves, one for water an one for the C/H with a Wilo pump. The water is heated by a Firebird Olympic S50/70 oil boiler. My issues are as follows:

1: We are unable to heat the hot water tank using the boiler (we are currently using the immersion), when H/W is selected the valve opens fine and the inlet pipe to the coil gets nice and hot. However, the water in the tank never gets hot enough to trip the tank thermostat (even when set low) , the boiler trips on its overheating stat first. The return pipe from the coil also never gets hot and when held doesn't feel like there is flow.

My initial thoughts were that there is a blockage in the coil???

2: The boiler trips on its thermostat sometimes when we have the heating on. The room stat works fine and turns the boiler off when it's at the required temp, but on occasion the boiler trips before the room stat. We have to manually reset the stat each time and upon removing the cover it is apparent that the boiler is hot.

Our boiler service man says the boiler stat is faulty and this will fix the tripping issue, however I am concerned that the two problems above are linked? If there is less flow due to a blocked coil would this cause the boiler to run hotter?

I have checked for air locks blending everything I can and have been up to the attic to check there is water in both tanks.

Should the blockage be cleared first? Wouldn't replacing the boiler stat, assuming it isn't cutting out soon enough (that's why it's overheating), cause the boiler to cut out potentially before the room stat?

I hope all this is clear I would be very greatful of any help.

Thank you in advance.
Connor

 

[SimonG]

Your boilerman sounds right, plus you may have an airlock in the cylinder coil. Have you had the system drained or partially drained recently?

 

[Resolute]

Have you had any work carried out at all recently or changes to the heating system (ie drained)?

Any other problems?

 

[dontknowitall]

Sorry, but going to pelt a few questions - I'm thinking the pump isn't working properly. Don't want to jump to conclusions though!

Is it an S or a Y plan? I'm assuming S plan. In case you don't know:
S Plan - flow from boiler (top pipe) goes to pump. Pipe after pump tees - one way for hot water via zone valve, other way for heating via another zone valve.
Y Plan - flow from boiler to pump. Then pipe to zone valve. One pipe to hot water other pipe to central heating. (Only 1 3-way zone valve with Y plan)

Does the central heating work properly?

Or when running do the upstairs radiators warm up and none of the downstairs radiators. If this is the case then the pump needs changing.

 

[diamondgas]

Being unable to heat the ho****er is a big isue IMO ... Circulation is your problem but the cause of the problem could be many things .... you realy need someone who knows there stuff!!!

Toss a dice or ask your neighbours ... good luck !

 

[Connor]

Thank you for the fast reply.

When we moved in (about 18 month ago) it was apparent that the C/H hadn't been used for a while as there was no oil. We got it going and had the problems. Last winter we ran out of oil and the system was left for a couple of weeks, when we started it we had a leaking pipe. I partially drained the system then?!?

 

[Best]

The boiler will not run hotter if less flow through coil, - boiler will just heat up quicker & cut off on boiler stat, or boiler limit stat if control stat faulty. I am guessing that your coil, or more likely, fittings at it are nearly blocked with dirt also. If the return pipe goes into a tee, I would start there.

 

[Best]

If you wanted to test if pipes/fittings near coil are blocked, then turn heating on & when coil flow starts heating up, tap fittings/ pipes gently with something blunt faced that won't do any damage. You may notice flow suddenly getting a lot hotter.

 

[Connor]

Sorry, but going to pelt a few questions - I'm thinking the pump isn't working properly. Don't want to jump to conclusions though!

Is it an S or a Y plan? I'm assuming S plan. In case you don't know:
S Plan - flow from boiler (top pipe) goes to pump. Pipe after pump tees - one way for hot water via zone valve, other way for heating via another zone valve.
Y Plan - flow from boiler to pump. Then pipe to zone valve. One pipe to hot water other pipe to central heating. (Only 1 3-way zone valve with Y plan)

Does the central heating work properly?

Or when running do the upstairs radiators warm up and none of the downstairs radiators. If this is the case then the pump needs changing.

Yes it is an 'S' plan system.

The C/H works Ok except for the boiler tripping out as mentioned.

All rads heat up fine, although one of them needs blending every few weeks.

Thank you.

 

[dontknowitall]

Pump is fine and zone valve for central heating is fine.

If you set the boiler for hot water does the pipe get hot before the zone valve but not so hot after (or near the hot water cylinder)? If so, push lever of zone valve to the right and lock it in place. Does this make a difference? If so then the motor in the zone valve needs changing.

 

[Connor]

Pump is fine and zone valve for central heating is fine.

If you set the boiler for hot water does the pipe get hot before the zone valve but not so hot after (or near the hot water cylinder)? If so, push lever of zone valve to the right and lock it in place. Does this make a difference? If so then the motor in the zone valve needs changing.

The pipe from the valve into the cylinder (coil) gets real hot when selected, the pipe from the cylinder (coil return) doesn't get very hot. This is what made me think there was a blockage in the coil. The boiler will trip out before the tank stat reaches the desired temp to close the valve. How long should it take to reach the average temp of the tank and what is the standard temp to set the H/W to?

 

[diamondgas]

I'd agree regards blockage/restriction in the h/w circuit. Idealy a temp diff of 11-20degC between F&R pipes, more than this indicates a slowing down. Ideal temp is 65DegC for stored water i believe, thereabouts.. 🙂

 

[Best]

Copper cylinder should come to heat from cold in half an hour ideally, but allow an hour. Return cool from coil can mean any of the 2 pipes are blocked. Just because flow is very hot, doesnt mean water is flowing well through it.